net: hns: register phy device in each mac initial sequence

In ACPI case, there is no interface to register phy device to mdio-bus.
Phy device has to be registered itself to mdio-bus, and then enet can
get the phy device's info so that it can config the phy-device to help
to trasmit and receive data.
HNS hardware topology is as below. The MDIO controller may control several
PHY-devices, and each PHY-device connects to a MAC device. PHY-devices
will register when each mac find PHY device in initial sequence.

                       cpu
                        |
                        |
     -------------------------------------------
    |                   |                       |
    |                   |                       |
    |                  dsaf                     |
   MDIO                 |                      MDIO
    |      ---------------------------          |
    |     |         |         |       |         |
    |     |         |         |       |         |
    |    MAC       MAC       MAC     MAC        |
    |     |         |         |       |         |
     ---- |-------- |-------- |       | --------
         ||        ||        ||       ||
         PHY       PHY       PHY     PHY

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>