UPSTREAM: loop: allow user to set the queue depth

Instead of hardcoding queue depth allow user to set the hw queue depth
using module parameter. Set default value to 128 to retain the existing
behavior.

Signed-off-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Link: https://lore.kernel.org/r/20220215213310.7264-5-kch@nvidia.com


Signed-off-by: Jens Axboe <axboe@kernel.dk>
Bug: 265019048
Change-Id: I03cd1f6e36347dbe94ffc2aeb2ef50454a713864
(cherry picked from commit ef44c508)
Signed-off-by: Bart Van Assche <bvanassche@google.com>