drm/amd/display: Get visual confirm color for stream

drm/amd/display: Get visual confirm color for stream

[WHY]
We want to output visual confirm color based on stream.

[HOW]
If visual confirm is for DMUB, use DMUB to get color.
Otherwise, find plane with highest layer index, output visual confirm color
of pipe that contains plane with highest index.

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Leo Zeng <Leo.Zeng@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>