* Broadcom UniMAC MDIO bus controller

Required properties:
- compatible: should one from "brcm,genet-mdio-v1", "brcm,genet-mdio-v2",
  "brcm,genet-mdio-v3", "brcm,genet-mdio-v4", "brcm,genet-mdio-v5" or
  "brcm,unimac-mdio"
- reg: address and length of the register set for the device, first one is the
  base register, and the second one is optional and for indirect accesses to
  larger than 16-bits MDIO transactions
- reg-names: name(s) of the register must be "mdio" and optional "mdio_indir_rw"
- #size-cells: must be 1
- #address-cells: must be 0

Optional properties:
- interrupts: must be one if the interrupt is shared with the Ethernet MAC or
  Ethernet switch this MDIO block is integrated from, or must be two, if there
  are two separate interrupts, first one must be "mdio done" and second must be
  for "mdio error"
- interrupt-names: must be "mdio_done_error" when there is a share interrupt fed
  to this hardware block, or must be "mdio_done" for the first interrupt and
  "mdio_error" for the second when there are separate interrupts
- clocks: A reference to the clock supplying the MDIO bus controller
- clock-frequency: the MDIO bus clock that must be output by the MDIO bus
  hardware, if absent, the default hardware values are used

Child nodes of this MDIO bus controller node are standard Ethernet PHY device
nodes as described in Documentation/devicetree/bindings/net/phy.txt

Example:

mdio@403c0 {
	compatible = "brcm,unimac-mdio";
	reg = <0x403c0 0x8 0x40300 0x18>;
	reg-names = "mdio", "mdio_indir_rw";
	#size-cells = <1>;
	#address-cells = <0>;

	...
	phy@0 {
		compatible = "ethernet-phy-ieee802.3-c22";
		reg = <0>;
	};
};