scsi: qla2xxx: Cleanup ELS/PUREX iocb fields

This patch does the following to improve RDP processing:

 - Rename field port_id to d_id in ELS and PUREX iocb structs to match FW
   spec.

 - Remove redundant comments from ELS and PUREX iocb structs.

 - Refactor fields in ELS iocb struct for error subcode common access.

 - Properly use error subcode fields in rdp processing routine.

 - Add print logs for alloc failure in purex rdp processing routine.

Link: https://lore.kernel.org/r/20200212214436.25532-13-hmadhani@marvell.com


Signed-off-by: Joe Carnuccio <joe.carnuccio@cavium.com>
Signed-off-by: Himanshu Madhani <hmadhani@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>