Properties for the MDIO bus multiplexer/glue of Amlogic G12a SoC family.

This is a special case of a MDIO bus multiplexer. It allows to choose between
the internal mdio bus leading to the embedded 10/100 PHY or the external
MDIO bus.

Required properties in addition to the generic multiplexer properties:
- compatible : amlogic,g12a-mdio-mux
- reg: physical address and length of the multiplexer/glue registers
- clocks: list of clock phandle, one for each entry clock-names.
- clock-names: should contain the following:
  * "pclk"   : peripheral clock.
  * "clkin0" : platform crytal
  * "clkin1" : SoC 50MHz MPLL

Example :

mdio_mux: mdio-multiplexer@4c000 {
	compatible = "amlogic,g12a-mdio-mux";
	reg = <0x0 0x4c000 0x0 0xa4>;
	clocks = <&clkc CLKID_ETH_PHY>,
		 <&xtal>,
		 <&clkc CLKID_MPLL_5OM>;
	clock-names = "pclk", "clkin0", "clkin1";
	mdio-parent-bus = <&mdio0>;
	#address-cells = <1>;
	#size-cells = <0>;

	ext_mdio: mdio@0 {
		reg = <0>;
		#address-cells = <1>;
		#size-cells = <0>;
	};

	int_mdio: mdio@1 {
		reg = <1>;
		#address-cells = <1>;
		#size-cells = <0>;

		internal_ephy: ethernet-phy@8 {
			compatible = "ethernet-phy-id0180.3301",
				     "ethernet-phy-ieee802.3-c22";
			interrupts = <GIC_SPI 9 IRQ_TYPE_LEVEL_HIGH>;
			reg = <8>;
			max-speed = <100>;
		};
	};
};