drm/amd/display: Change Brightness Control Priority

Prioritize Aux-based over PWM-based brightness control
for more types of panels and introduce a new structure
to store and manage the type of brightness control used.

Reviewed-by: Anthony Koo <anthony.koo@amd.com>
Signed-off-by: Muyuan Yang <muyuan.yang@amd.com>
Signed-off-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>