habanalabs: expose a single cs seq in staged submissions

Staged submission consists of multiple command submissions.
In order to be explicit, driver should return a single cs sequence
for every cs in the submission, or else user may try to wait on
an internal CS rather than waiting for the whole submission.

Signed-off-by: Ofir Bitton <obitton@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>