APM X-Gene SoC Ethernet nodes

Ethernet nodes are defined to describe on-chip ethernet interfaces in
APM X-Gene SoC.

Required properties for all the ethernet interfaces:
- compatible: Should be "apm,xgene-enet"
- reg: Address and length of the register set for the device. It contains the
  information of registers in the same order as described by reg-names
- reg-names: Should contain the register set names
  - "enet_csr": Ethernet control and status register address space
  - "ring_csr": Descriptor ring control and status register address space
  - "ring_cmd": Descriptor ring command register address space
- interrupts: Ethernet main interrupt
- clocks: Reference to the clock entry.
- local-mac-address: MAC address assigned to this device
- phy-connection-type: Interface type between ethernet device and PHY device

Required properties for ethernet interfaces that have external PHY:
- phy-handle: Reference to a PHY node connected to this device

- mdio: Device tree subnode with the following required properties:
  - compatible: Must be "apm,xgene-mdio".
  - #address-cells: Must be <1>.
  - #size-cells: Must be <0>.

  For the phy 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.

Optional properties:
- status: Should be "ok" or "disabled" for enabled/disabled. Default is "ok".

Example:
	menetclk: menetclk {
		compatible = "apm,xgene-device-clock";
		clock-output-names = "menetclk";
		status = "ok";
	};

	menet: ethernet@17020000 {
		compatible = "apm,xgene-enet";
		status = "disabled";
		reg = <0x0 0x17020000 0x0 0xd100>,
		      <0x0 0X17030000 0x0 0X400>,
		      <0x0 0X10000000 0x0 0X200>;
		reg-names = "enet_csr", "ring_csr", "ring_cmd";
		interrupts = <0x0 0x3c 0x4>;
		clocks = <&menetclk 0>;
		local-mac-address = [00 01 73 00 00 01];
		phy-connection-type = "rgmii";
		phy-handle = <&menetphy>;
		mdio {
			compatible = "apm,xgene-mdio";
			#address-cells = <1>;
			#size-cells = <0>;
			menetphy: menetphy@3 {
				compatible = "ethernet-phy-id001c.c915";
				reg = <0x3>;
			};

		};
	};

/* Board-specific peripheral configurations */
&menet {
        status = "ok";
};