drm/amd/display: reduce abm min reduction, deviation gain and contrast factor

[Why]
Increased power savings are desired for ABM 2.2.

[How]
Reduce the minimum reduction level, the deviation gain and the contrast factor
to allow for more aggressive operation of the algorithm.

Signed-off-by: Josip Pavic <Josip.Pavic@amd.com>
Reviewed-by: Anthony Koo <Anthony.Koo@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>