drm/amd/display: Define PSR ERROR Status bit VSC_SDP

[why]
So we can track VSC SDP errors from display

[how]
Define the bit, and use it in driver logic

Signed-off-by: Reza Amini <Reza.Amini@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>