drm/nv10: fix chipset checks, mostly for the benefit of nv1a

NV1A is numerically higher than NV17 but generationally lower. Use the
new card type to help disambiguate.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>