drm/amd/display: add vsc update support for test pattern request

drm/amd/display: add vsc update support for test pattern request

[how]
Allow vsc info packet if vsc is supported.  Update vsc based on test
pattern request.  Remove dpg_is_blanked polling, apply hardware global
lock instead to ensure double buffered dpg is updated with vsc in one
frame

Signed-off-by: Wenjing Liu <Wenjing.Liu@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>