[Why]
When rapidly adjusting color temperature, screen tearing was observed.
This was due to overwritten values in gamut remap registers.
This issue was solved for OCSC and ICSC by alternating between "A" and
"B" registers to double buffer the writes.

[How]
Create new set_gamut_remap and program_gamut_remap for dcn20.
Alternate which registers are written to by switching modes each time.
Also fixes ICSC mode reg read to use proper data offset.
Signed-off-by: Noah Abradjian <noah.abradjian@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>