scsi: hisi_sas: relocate some common code for v3 hw

Much code of PM suspend function also exists in soft reset function. This
is not concise. So, this patch relocates the common code of these two
functions to a separate function.

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