nv50: allow non-nv12 buffers to be created, just pass them through to vl

Since we expose non-NV12 formats as supported when there is no decoer
profile selected, make sure that those formats are actually allowed to
be allocated.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "9.2" <mesa-stable@lists.freedesktop.org>