drm/amd/display: Add double buffer machanism to ICSC

drm/amd/display: Add double buffer machanism to ICSC

- Video playback shows tearing when adjusting
brightness through radeon custom settings.
- Now added double buffer mechanism to switch
input CSC from register buffer ICSC and COMA
- Improved tab alignment

Signed-off-by: Xingyue Tao <xingyue.tao@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>