Improve Performance in Higher Presets

Description

Switch M7+ to 6L. Improve bd-rate/speed tradeoffs for all presets.

Issue

Author(s)

@PhoenixWorth @dxyliu @mann-c

Performance impact

Preset	PSNR	SSIM	VMAF	SPEED DEV	MEMORY DEV
1	-0.24%	-0.28%	-0.16%	1.76%	-0.09%
2	-0.20%	-0.24%	-0.11%	-0.14%	-0.05%
3	-0.20%	-0.24%	-0.15%	-1.51%	0.01%
4	-0.24%	-0.25%	-0.16%	-1.17%	0.10%
5	-0.14%	-0.11%	-0.10%	2.49%	6.35%
6	-0.99%	-0.91%	-0.75%	3.81%	-1.61%
7	-1.20%	-2.47%	-0.87%	-10.67%	-35.45%
8	-0.97%	-2.07%	-1.21%	-6.34%	-34.25%
9	-1.03%	-1.63%	-1.27%	1.28%	-33.23%
10	-0.38%	-1.18%	-0.66%	1.84%	-33.93%
11	0.23%	-0.51%	-0.49%	1.02%	-36.44%
12	0.96%	0.06%	-0.14%	-0.69%	-33.77%
13	-1.85%	-1.39%	-0.05%	-2.27%	0.01%

• quality
• memory
• speed
• 8 bit
• 10 bit
• N/A

Test set

• obj-1-fast can be found here
• other
• [] N/A

Merge method

• Allow the maintainer to squash and merge when PR is ready to create a 1-commit to the master branch. The maintainer will be able to fix typos / combine commit messages to create a more readable 1-commit message or use whatever is stated in the 'Description' section
• I will clean up my commits and the maintainer shall use 'rebase and merge' to the master branch