hisi_sas: add v2 hw support for >4 SATA phys

This patch adds support for directly attaching SATA disks to phy
4-8. The problem was that only registers concerned with phy 0-3 were
being considered in sata_int_v2_hw().  The issue was not detected
previously as the development board only exposed phy 0-3; the new board
provides access to 8 phys.

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>