nouveau: fix chipset checks for nv1a by using the oclass instead

Commit f4ebcd133b9 ("dri/nouveau: NV17_3D class is not available for
NV1a chipset") fixed this partially by using the correct 3d class.
However there were a lot of checks left over comparing against the
chipset.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>