scsi: qla2xxx: Add ability to send PRLO

Add ability to send Implicit PRLO to flush IOs
from FW back to driver.

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>