scsi: hisi_sas: Add helper to process bcast events

Add a helper for bcast processing to reduce duplication.

Link: https://lore.kernel.org/r/1662378529-101489-5-git-send-email-john.garry@huawei.com


Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>