drm/amd/display: For vblank_disable_immediate, check PSR is really used

Even if PSR is allowed for a present GPU, there might be no eDP link
which supports PSR.

Fixes: 70897848

 ("drm/amdgpu/display: Only set vblank_disable_immediate when PSR is not enabled")
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Michel Dänzer <mdaenzer@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>