scsi: hisi_sas: add phy_set_linkrate_v3_hw()

Add function to set linkrate 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>