habanalabs: get multiple fences under same cs_lock

To add proper support for wait-for-multi-CS, locking the CS lock
for each CS fence in the list is not efficient.

Instead, this patch add support to lock the CS lock once to get all
required fences.

Signed-off-by: Ohad Sharabi <osharabi@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>