Add bsg interface for app to read doorbell events. This interface lets
driver know how much app can read based on return buffer size. When the
next event(s) occur, driver will return the bsg_job with the event(s) in
the return buffer.

If there is no event to read, driver will hold on to the bsg_job up to few
seconds as a way to control the polling interval.

Link: https://lore.kernel.org/r/20220607044627.19563-5-njavali@marvell.com
Fixes: dd30706e ("scsi: qla2xxx: edif: Add key update")
Signed-off-by: Quinn Tran <qutran@marvell.com>
Signed-off-by: Nilesh Javali <njavali@marvell.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>