drm/amd/pm: Disable GFXOFF when GFX DPM or PG disabled

Check GFX DPM and PG bit before enable GFXOFF on Vangogh
smu post init.

Signed-off-by: Jinzhou Su <Jinzhou.Su@amd.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>