scsi: qla2xxx: Move heartbeat handling from DPC thread to workqueue

scsi: qla2xxx: Move heartbeat handling from DPC thread to workqueue

DPC thread gets restricted due to a no-op mailbox, which is a blocking call
and has a high execution frequency. To free up the DPC thread we move no-op
handling to the workqueue. Also, modified qla_do_heartbeat() to send no-op
MBC if we don’t have any active interrupts, but there are still I/Os
outstanding with firmware.

Link: https://lore.kernel.org/r/20210908164622.19240-9-njavali@marvell.com
Fixes: 6874cad05532 ("scsi: qla2xxx: Add heartbeat check")
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Signed-off-by: Manish Rangankar <mrangankar@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>