drm/amd/display: Add visual confirm color support for SubVP

[Why && How]
We would like to have visual confirm color support for SubVP.
	1. Set visual confirm color to red: SubVP is enable on this
	display;
	2. Set visual confirm color to green: SubVP is enable on
	other display and DRR is on this display;
	3. Set visual confirm color to blue: SubVP is enable on
	other display and DRR is off on this display;

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Brian Chang <Brian.Chang@amd.com>
Signed-off-by: Leo (Hanghong) Ma <hanghong.ma@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>