drm/nouveau: block a bunch of classes from userspace

Long ago, there had been plans for making use of a bunch of these APIs
from userspace and there's various checks in place to stop misbehaving.

Countless other projects have occurred in the meantime, and the pieces
didn't finish falling into place for that to happen.

They will (hopefully) in the not-too-distant future, but it won't look
quite as insane.  The super checks are causing problems right now, and
are going to be removed.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>