scsi: hisi_sas: some optimizations of host controller reset

This patch do following optimizations to host controller reset:

1. Unblock scsi requests before rescanning topology, as SCSI command need be
   used if new device is found during rescanning topology.

2. Remove drain_workqueue(hisi_hba->wq) and drain_workqueue(shost->work_q), as
   there is no need to ensure that all PHYs event are done before exiting host
   reset.

3. Improve message print level of host reset. Host reset is an important and
   very few occurrence event. We should know its progress even when not
   debugging.

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>