drm/nouveau/fifo/tu102: Move Turing specific FIFO functions

Turing requires some changes to FIFO interrupt handling due to changes
in HW register layout. It also requires some changes to implement robust
channel (RC) recovery. This preparatory patch moves the functions
requiring changes into nvkm/engine/fifo/tu102.c so they can be altered
without affecting gk104 and other users. It should not introduce any
functional changes.

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