Documentation: dtb: xgene: Add MDIO node

APM X-Gene SoC MDIO node

MDIO node is defined to describe on-chip MDIO controller.

Required properties:

	- compatible: Must be "apm,xgene-mdio-rgmii" or "apm,xgene-mdio-xfi"

	- #address-cells: Must be <1>.

	- #size-cells: Must be <0>.

	- reg: Address and length of the register set

	- clocks: Reference to the clock entry

For the phys on the mdio bus, there must be a node with the following fields:

	- compatible: PHY identifier.  Please refer ./phy.txt for the format.

	- reg: The ID number for the phy.

Example:

	mdio: mdio@17020000 {

		compatible = "apm,xgene-mdio-rgmii";

		#address-cells = <1>;

		#size-cells = <0>;

		reg = <0x0 0x17020000 0x0 0xd100>;

		clocks = <&menetclk 0>;

	};

	/* Board-specific peripheral configurations */

	&mdio {

		menetphy: phy@3 {

			reg = <0x3>;

		};

		sgenet0phy: phy@4 {

			reg = <0x4>;

		};

		sgenet1phy: phy@5 {

			reg = <0x5>;

		};

	};