drm/amd/display: Workaround IGT multiplane restriction

IGT currently does not properly commit changes on planes with multiple
possible CRTC's. Set one valid CRTC for each plane for now, plus one
underlay plane on Carizzo and Stoney that is valid for all CRTCs.

Signed-off-by: Leo (Sunpeng) Li <sunpeng.li@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>