net: hns: select Hilink before serdes loopback for HNS V2

As Hilink3 and Hilink4 use the same xge training and xge u adaptor for
HNSv2, it needs to select which Hilink to be set before relative serdes
being configed. The hilink_access_sel is the register to do that.

Signed-off-by: Kejian Yan <yankejian@huawei.com>
Signed-off-by: Yisen Zhuang <Yisen.Zhuang@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>