drm/nouveau/mmu/nv4a: use nv04 mmu rather than the nv44 one

drm/nouveau/mmu/nv4a: use nv04 mmu rather than the nv44 one

The NV4A (aka NV44A) is an oddity in the family. It only comes in AGP
and PCI varieties, rather than a core PCIE chip with a bridge for
AGP/PCI as necessary. As a result, it appears that the MMU is also
non-functional. For AGP cards, the vast majority of the NV4A lineup,
this worked out since we force AGP cards to use the nv04 mmu. However
for PCI variants, this did not work.

Switching to the NV04 MMU makes it work like a charm. Thanks to mwk for
the suggestion. This should be a no-op for NV4A AGP boards, as they were
using it already.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=70388
Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: stable@vger.kernel.org
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>