scsi: qla2xxx: Add support for mailbox passthru

This interface will allow user space applications to send a mailbox command
to the firmware.

Link: https://lore.kernel.org/r/20210908164622.19240-2-njavali@marvell.com


Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Bikash Hazarika <bhazarika@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>