At unload time, we need to disable DRPS, but we need to do it correctly
or the GPU will hang and we won't be able to load the module again.  So
set the SFCAVM bit so we can properly restore the DRPS config at unload.
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: NEric Anholt <eric@anholt.net>