nouveau/gsp: add a 50ms delay between fbsr and driver unload rpcs

This fixes a bunch of command hangs after runtime suspend/resume.

This fixes a regression caused by code movement in the commit below,
the commit seems to just change timings enough to cause this to happen
now, and adding the sleep seems to avoid it.

I've spent some time trying to root cause it to no great avail,
it seems like a bug on the firmware side, but it could be a bug
in our rpc handling that I can't find.

Either way, we should land the workaround to fix the problem,
while we continue to work out the root cause.

Signed-off-by: Dave Airlie <airlied@redhat.com>
Cc: Ben Skeggs <bskeggs@nvidia.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Fixes: c21b0397 ("drm/nouveau/gsp: add hals for fbsr.suspend/resume()")
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
Link: https://lore.kernel.org/r/20250702232707.175679-1-airlied@gmail.com