drm/nouveau/fifo/gk104-: identify mmu engine ids for host faults

It appears these don't map to PBDMAs (at least on Kepler, it may or may
be valid for Fermi - this hasn't been checked), but to runlists.

This drops the NVKM_ENGINE_FIFO data from the entries too, as resetting
all of PFIFO is *not* the way to handle such faults.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>