drm/amd/display: Allow PState switch in VBLANK one display VACTIVE

[Why]
For certain display configurations we want to allow PSTATE
switch when one display can switch in VACTIVE and the
other display can switch in VBLANK

[How]
Add extra condition to dcn2 pstate support check

Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>