lg-hamerhead: fix X11 UIs based on frammebuffer driver

Xorg was segfaulting on all installs involving Xorg; this adds Driver "fbdev" to xorg.conf, solving the segfault found in this discussion.. After that, the system booted but the display was frozen, adding msm-fb-refresher to X11 dependencies in APKBUILD solved this (though it is considered hacky. Tested on lg-hammerhead; installs with i3wm and xfce now work.