scsi: qedf: Add change_queue_depth member to scsi_host_template().

Add the change_queue_depth member to our SCSI host template so the queue
depth of devices attached to qedf can be changed dynamically.

Signed-off-by: Chad Dupuis <chad.dupuis@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>