drm/amd/display: Fix double buffering in dcn2 ICSC

[Why]
When rapidly adjusting video brightness, screen tearing was observed.
This was due to overwritten values in ICSC registers. In dcn10, this issue had been
fixed by implementing double buffering via alternating ICSC modes.
However, the second register set used in dcn1 doesn't exist in dcn2.

[How]
Create new program_input_csc for dcn20.
Use ICSC_B registers instead of COMA registers as second set.

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>