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

Now have a somewhat simpler semaphore sync implementation for nv17:nv84,
and a switched to using semaphores as fences on nv84+ and making use of
the hardware's >= acquire operation.
Signed-off-by: NBen Skeggs <bskeggs@redhat.com>