drm/amdgpu: add AVFS control to PP_FEATURE_MASK

Add a ppfeaturemask flag to disable AVFS control.

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