drm/amd/display: add visual confirm colors to differentiate layer_index > 0

[WHY]
Currently there is no way to visually identify if there is one or more
layers presented fullscreen on the display

[HOW]
Add new visual confirm colors in get_surface_visual_confirm_color for
planes with layer_index > 0

Signed-off-by: Evgenii Krasnikov <Evgenii.Krasnikov@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Stylon Wang <stylon.wang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>