scsi: libsas: Add helper for port add ex_phy

This moves the process of adding ex_phy to a port into a new helper.

Signed-off-by: Xingui Yang <yangxingui@huawei.com>
Link: https://lore.kernel.org/r/20240312141103.31358-2-yangxingui@huawei.com


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