Hisilicon Fast Ethernet MDIO Controller interface

Required properties:
- compatible: should be "hisilicon,hisi-femac-mdio".
- reg: address and length of the register set for the device.
- clocks: A phandle to the reference clock for this device.

- PHY subnode: inherits from phy binding [1]
[1] Documentation/devicetree/bindings/net/phy.txt

Example:
mdio: mdio@10091100 {
	compatible = "hisilicon,hisi-femac-mdio";
	reg = <0x10091100 0x10>;
	clocks = <&crg HI3516CV300_MDIO_CLK>;
	#address-cells = <1>;
	#size-cells = <0>;

	phy0: phy@1 {
		reg = <1>;
	};
};