drm/nouveau/mc/tu102: Fix MMU fault interrupts on Turing

Turing reports MMU fault interrupts via new top level interrupt
registers. The old PMC MMU interrupt vector is not used by the HW. This
means we can remap the new top-level MMU interrupt to the exisiting PMC
MMU bit which simplifies the implementation until all interrupts are
moved over to using the new top level registers.

Signed-off-by: Alistair Popple <apopple@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>