scsi: tcm_loop: Allow queues, can_queue and cmd_per_lun to be settable

Make can_queue, nr_hw_queues and cmd_per_lun settable by the user instead
of hard coding them.

Link: https://lore.kernel.org/r/1604257174-4524-9-git-send-email-michael.christie@oracle.com


Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Mike Christie <michael.christie@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>