net: hix5hd2_gmac: add reset control and clock signals

Add three reset control signals, "mac_core_rst", "mac_ifc_rst" and
"phy_rst".
The following diagram explained how the reset signals work.

                        SoC
|-----------------------------------------------------
|                               ------                |
|                               | cpu |               |
|                               ------                |
|                                  |                  |
|                              ------------ AMBA bus  |
|                         GMAC     |                  |
|                            ----------------------   |
| ------------- mac_core_rst | --------------      |  |
| |clock and   |-------------->|   mac core  |     |  |
| |reset       |             | --------------      |  |
| |generator   |----         |       |             |  |
| -------------     |        | ----------------    |  |
|          |        ---------->| mac interface |   |  |
|          |     mac_ifc_rst | ----------------    |  |
|          |                 |       |             |  |
|          |                 | ------------------  |  |
|          |phy_rst          | | RGMII interface | |  |
|          |                 | ------------------  |  |
|          |                 ----------------------   |
|----------|------------------------------------------|
           |                          |
           |                      ----------
           |--------------------- |PHY chip |
                                  ----------

The "mac_core_rst" represents "mac core reset signal", it resets
the mac core including packet processing unit, descriptor processing unit,
tx engine, rx engine, control unit.
The "mac_ifc_rst" represents "mac interface reset signal", it resets
the mac interface. The mac interface unit connects mac core and
data interface like MII/RMII/RGMII. After we set a new value of
interface mode, we must reset mac interface to reload the new mode value.
The "mac_core_rst" and "mac_ifc_rst" are both optional to be
backward compatible with the hix5hd2 SoC.
The "phy_rst" represents "phy reset signal", it does a hardware reset
on the PHY chip. This reset signal is optional if the PHY can work well
without the hardware reset.

Add one more clock signal, the existing is MAC core clock,
and the new one is MAC interface clock.
The MAC interface clock is optional to be backward compatible with
the hix5hd2 SoC.

Signed-off-by: Dongpo Li <lidongpo@hisilicon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>