* Marvell MDIO Ethernet Controller interface

The Ethernet controllers of the Marvel Kirkwood, Dove, Orion5x,
MV78xx0, Armada 370, Armada XP, Armada 7k and Armada 8k have an
identical unit that provides an interface with the MDIO bus.
Additionally, Armada 7k and Armada 8k has a second unit which
provides an interface with the xMDIO bus. This driver handles
these interfaces.

Required properties:
- compatible: "marvell,orion-mdio" or "marvell,xmdio"
- reg: address and length of the MDIO registers.  When an interrupt is
  not present, the length is the size of the SMI register (4 bytes)
  otherwise it must be 0x84 bytes to cover the interrupt control
  registers.

Optional properties:
- interrupts: interrupt line number for the SMI error/done interrupt
- clocks: phandle for up to three required clocks for the MDIO instance

The child nodes of the MDIO driver are the individual PHY devices
connected to this MDIO bus. They must have a "reg" property given the
PHY address on the MDIO bus.

Example at the SoC level without an interrupt property:

mdio {
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "marvell,orion-mdio";
	reg = <0xd0072004 0x4>;
};

Example with an interrupt property:

mdio {
	#address-cells = <1>;
	#size-cells = <0>;
	compatible = "marvell,orion-mdio";
	reg = <0xd0072004 0x84>;
	interrupts = <30>;
};

And at the board level:

mdio {
	phy0: ethernet-phy@0 {
		reg = <0>;
	};

	phy1: ethernet-phy@1 {
		reg = <1>;
	};
}