main/linux-postmarketos-allwinner: change gpu clock to 500mhz

This pull request clocks the GPU at 500 MHz, which gives better GPU performance.

Here is glmark2 running for comparison (test is done on Pinetab running swaywm):

#################
423 MHZ::: STOCK SPEED
#################
pine64-pinetab:~$ XDG_RUNTIME_DIR=/run/user/10000 glmark2-es2-wayland
=======================================================
    glmark2 2020.04
=======================================================
    OpenGL Information
    GL_VENDOR:     lima
    GL_RENDERER:   Mali400
    GL_VERSION:    OpenGL ES 2.0 Mesa 20.2.0-devel
=======================================================
[build] use-vbo=false: FPS: 318 FrameTime: 3.145 ms
[build] use-vbo=true: FPS: 365 FrameTime: 2.740 ms
[texture] texture-filter=nearest: FPS: 445 FrameTime: 2.247 ms
[texture] texture-filter=linear: FPS: 430 FrameTime: 2.326 ms
[texture] texture-filter=mipmap: FPS: 453 FrameTime: 2.208 ms
[shading] shading=gouraud: FPS: 238 FrameTime: 4.202 ms
[shading] shading=blinn-phong-inf: FPS: 177 FrameTime: 5.650 ms
[shading] shading=phong: FPS: 124 FrameTime: 8.065 ms
[shading] shading=cel: FPS: 80 FrameTime: 12.500 ms
[bump] bump-render=high-poly: FPS: 103 FrameTime: 9.709 ms
[bump] bump-render=normals: FPS: 254 FrameTime: 3.937 ms
[bump] bump-render=height: FPS: 191 FrameTime: 5.236 ms
[effect2d] kernel=0,1,0;1,-4,1;0,1,0;: FPS: 67 FrameTime: 14.925 ms
[effect2d] kernel=1,1,1,1,1;1,1,1,1,1;1,1,1,1,1;: FPS: 32 FrameTime: 31.250 ms
[pulsar] light=false:quads=5:texture=false: FPS: 585 FrameTime: 1.709 ms
[desktop] blur-radius=5:effect=blur:passes=1:separable=true:windows=4: FPS: 24 FrameTime: 41.667 ms
[desktop] effect=shadow:windows=4: FPS: 179 FrameTime: 5.587 ms
[buffer] columns=200:interleave=false:update-dispersion=0.9:update-fraction=0.5:update-method=map: FPS: 64 FrameTime: 15.625 ms
[buffer] columns=200:interleave=false:update-dispersion=0.9:update-fraction=0.5:update-method=subdata: FPS: 63 FrameTime: 15.873 ms
[buffer] columns=200:interleave=true:update-dispersion=0.9:update-fraction=0.5:update-method=map: FPS: 88 FrameTime: 11.364 ms
[ideas] speed=duration: FPS: 92 FrameTime: 10.870 ms
[jellyfish] <default>: FPS: 62 FrameTime: 16.129 ms
Error: SceneTerrain requires Vertex Texture Fetch support, but GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS is 0
[terrain] <default>: Unsupported
[shadow] <default>: FPS: 104 FrameTime: 9.615 ms
[refract] <default>: FPS: 19 FrameTime: 52.632 ms
[conditionals] fragment-steps=0:vertex-steps=0: FPS: 276 FrameTime: 3.623 ms
[conditionals] fragment-steps=5:vertex-steps=0: FPS: 124 FrameTime: 8.065 ms
[conditionals] fragment-steps=0:vertex-steps=5: FPS: 278 FrameTime: 3.597 ms
[function] fragment-complexity=low:fragment-steps=5: FPS: 172 FrameTime: 5.814 ms
[function] fragment-complexity=medium:fragment-steps=5: FPS: 80 FrameTime: 12.500 ms
[loop] fragment-loop=false:fragment-steps=5:vertex-steps=5: FPS: 172 FrameTime: 5.814 ms
[loop] fragment-steps=5:fragment-uniform=false:vertex-steps=5: FPS: 172 FrameTime: 5.814 ms
[loop] fragment-steps=5:fragment-uniform=true:vertex-steps=5: FPS: 63 FrameTime: 15.873 ms
=======================================================
                                  glmark2 Score: 184 
=======================================================



#################
500 MHZ:::
#################
pine64-pinetab:~$ XDG_RUNTIME_DIR=/run/user/10000 glmark2-es2-wayland
=======================================================
    glmark2 2020.04
=======================================================
    OpenGL Information
    GL_VENDOR:     lima
    GL_RENDERER:   Mali400
    GL_VERSION:    OpenGL ES 2.0 Mesa 20.2.0-devel
=======================================================
[build] use-vbo=false: FPS: 348 FrameTime: 2.874 ms
[build] use-vbo=true: FPS: 417 FrameTime: 2.398 ms
[texture] texture-filter=nearest: FPS: 448 FrameTime: 2.232 ms
[texture] texture-filter=linear: FPS: 473 FrameTime: 2.114 ms
[texture] texture-filter=mipmap: FPS: 487 FrameTime: 2.053 ms
[shading] shading=gouraud: FPS: 248 FrameTime: 4.032 ms
[shading] shading=blinn-phong-inf: FPS: 196 FrameTime: 5.102 ms
[shading] shading=phong: FPS: 145 FrameTime: 6.897 ms
[shading] shading=cel: FPS: 95 FrameTime: 10.526 ms
[bump] bump-render=high-poly: FPS: 102 FrameTime: 9.804 ms
[bump] bump-render=normals: FPS: 299 FrameTime: 3.344 ms
[bump] bump-render=height: FPS: 226 FrameTime: 4.425 ms
[effect2d] kernel=0,1,0;1,-4,1;0,1,0;: FPS: 80 FrameTime: 12.500 ms
[effect2d] kernel=1,1,1,1,1;1,1,1,1,1;1,1,1,1,1;: FPS: 36 FrameTime: 27.778 ms
[pulsar] light=false:quads=5:texture=false: FPS: 616 FrameTime: 1.623 ms
[desktop] blur-radius=5:effect=blur:passes=1:separable=true:windows=4: FPS: 27 FrameTime: 37.037 ms
[desktop] effect=shadow:windows=4: FPS: 199 FrameTime: 5.025 ms
[buffer] columns=200:interleave=false:update-dispersion=0.9:update-fraction=0.5:update-method=map: FPS: 67 FrameTime: 14.925 ms
[buffer] columns=200:interleave=false:update-dispersion=0.9:update-fraction=0.5:update-method=subdata: FPS: 66 FrameTime: 15.152 ms
[buffer] columns=200:interleave=true:update-dispersion=0.9:update-fraction=0.5:update-method=map: FPS: 93 FrameTime: 10.753 ms
[ideas] speed=duration: FPS: 94 FrameTime: 10.638 ms
[jellyfish] <default>: FPS: 69 FrameTime: 14.493 ms
Error: SceneTerrain requires Vertex Texture Fetch support, but GL_MAX_VERTEX_TEXTURE_IMAGE_UNITS is 0
[terrain] <default>: Unsupported
[shadow] <default>: FPS: 118 FrameTime: 8.475 ms
[refract] <default>: FPS: 22 FrameTime: 45.455 ms
[conditionals] fragment-steps=0:vertex-steps=0: FPS: 329 FrameTime: 3.040 ms
[conditionals] fragment-steps=5:vertex-steps=0: FPS: 150 FrameTime: 6.667 ms
[conditionals] fragment-steps=0:vertex-steps=5: FPS: 330 FrameTime: 3.030 ms
[function] fragment-complexity=low:fragment-steps=5: FPS: 207 FrameTime: 4.831 ms
[function] fragment-complexity=medium:fragment-steps=5: FPS: 96 FrameTime: 10.417 ms
[loop] fragment-loop=false:fragment-steps=5:vertex-steps=5: FPS: 206 FrameTime: 4.854 ms
[loop] fragment-steps=5:fragment-uniform=false:vertex-steps=5: FPS: 206 FrameTime: 4.854 ms
[loop] fragment-steps=5:fragment-uniform=true:vertex-steps=5: FPS: 71 FrameTime: 14.085 ms
=======================================================
                                  glmark2 Score: 205 
=======================================================