scsi: hisi_sas: add host reset interface for test

Add host reset interface to make it easier for testing the host reset
feature.

Signed-off-by: Xiang Chen <chenxiang66@hisilicon.com>
Signed-off-by: John Garry <john.garry@huawei.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>