scsi: qla2xxx: Preparation for Target MQ.

In Current code, Req Q 0, RespQ 0 & hardware_lock are the main resources
for sending and process completion of Target IO. These resources are now
referenced behind a new qpair/"struct qla_qpair base_qpair".  Main path
IO handle will access those resources via the qpair pointer in
preparation for Target MQ.

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>