nouveau/gsp: handle engines in runl without nonstall interrupts.

It appears on TU106 GPUs (2070), that some of the nvdec engines
are in the runlist but have no valid nonstall interrupt, nouveau
didn't handle that too well.

This should let nouveau/gsp work on those.

Cc: stable@vger.kernel.org # v6.7+
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://lore.kernel.org/all/20240110011826.3996289-1-airlied@gmail.com/