scsi: hisi_sas: change queue depth from 512 to 4096

If sending IOs to many disks from single queue, it is possible that the
queue may be full. To avoid the situation, change queue depth from 512 to
4096 which is the max number of IOs for v3 hw.

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>