drm/nouveau/vdec: implement support for VP3 engines

For NV98+, BSP/VP/PPP are all FUC-based engines. Hook them all up in the
same way as NVC0, but with a couple of different values. Also make sure
that the PPP engine is handled in the fifo/mc/vm.

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