Micrel KSZ9021 Gigabit Ethernet PHY

Some boards require special tuning values, particularly when it comes to
clock delays.  You can specify clock delay values by adding
micrel-specific properties to an Ethernet OF device node.

All skew control options are specified in picoseconds.  The minimum
value is 0, and the maximum value is 3000.

Optional properties:
 - rxc-skew-ps : Skew control of RXC pad
 - rxdv-skew-ps : Skew control of RX CTL pad
 - txc-skew-ps : Skew control of TXC pad
 - txen-skew-ps : Skew control of TX_CTL pad
 - rxd0-skew-ps : Skew control of RX data 0 pad
 - rxd1-skew-ps : Skew control of RX data 1 pad
 - rxd2-skew-ps : Skew control of RX data 2 pad
 - rxd3-skew-ps : Skew control of RX data 3 pad
 - txd0-skew-ps : Skew control of TX data 0 pad
 - txd1-skew-ps : Skew control of TX data 1 pad
 - txd2-skew-ps : Skew control of TX data 2 pad
 - txd3-skew-ps : Skew control of TX data 3 pad

Examples:

	/* Attach to an Ethernet device with autodetected PHY */
	&enet {
		rxc-skew-ps = <3000>;
		rxdv-skew-ps = <0>;
		txc-skew-ps = <3000>;
		txen-skew-ps = <0>;
		status = "okay";
	};

	/* Attach to an explicitly-specified PHY */
	mdio {
		phy0: ethernet-phy@0 {
			rxc-skew-ps = <3000>;
			rxdv-skew-ps = <0>;
			txc-skew-ps = <3000>;
			txen-skew-ps = <0>;
			reg = <0>;
		};
	};
	ethernet@70000 {
		status = "okay";
		phy = <&phy0>;
		phy-mode = "rgmii-id";
	};