drm/nouveau: enable dynamic job-flow control

Make use of the scheduler's credit limit and scheduler job's credit
count to account for the actual size of a job, such that we fill up the
ring efficiently.

Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231114002728.3491-2-dakr@redhat.com