drm/amd/display: Fix test pattern color space inconsistency for Linux

[why]
When reprogram MSA with updated color space, the test color space shows
inconsistency. Linux has separate routine to set up test pattern color
space, but it fails to configure RGB.

[How]
Add RGB to test pattern.

Fixes: 43563bc2

 ("drm/amd/display: update MSA and VSC SDP on video test pattern request")
Signed-off-by: Jerry (Fangzhi) Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Hersen Wu <hersenxs.wu@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>