Thead light/ice DWMAC glue layer controller

This file documents platform glue layer for stmmac.
Please see stmmac.txt for the other unchanged properties.

The device node has following properties.

Required properties:
- compatible:  should be "thead,light-dwmac" for light glue,
	       and "thead,ice-dwmac" for ice glue.
- clocks: Must contain a phandle for each entry in clock-names.
- clock-names: Should be "stmmaceth" for the host clock.
	       Should be "gmac_pll_clk" for the MAC TX clock.
- reg/reg-names: "gmac" is required for controller registers.
- interrupt-names: Should contain a list of interrupt names corresponding to
               the interrupts in the interrupts property, if available.
	       Should be "macirq" for the main MAC IRQ

Optional properties:
- reg/reg-names: "phy_if_reg"/"txclk_dir_reg"/"clk_mgr_reg" is optional,
                 which is to control interface mode, txclk direction and clock
                 setting in soc glue layer.
- rx-clk-delay : set this property for RGMII rx clk delay setting in MAC.
- tx-clk-delay : set this property for RGMII tx clk delay setting in MAC.

Example:
	gmac: ethernet@ffe7070000 {
		compatible = "thead,light-dwmac";
		reg = <0xff 0xe7070000 0x0 0x2000
		       0xff 0xe703001c 0x0 0x4
		       0xff 0xe7030020 0x0 0x4
		       0xff 0xe7030000 0x0 0x1c>;
		reg-names = "gmac", "phy_if_reg", "txclk_dir_reg", "clk_mgr_reg";
		interrupt-parent = <&intc>;
		interrupts = <66>;
		interrupt-names = "macirq";
		clocks = <&dummy_ahb>, <&dummy_clock_gmac>;
		clock-names = "stmmaceth", "gmac_pll_clk";
		snps,pbl = <32>;
		snps,fixed-burst;
		phy-mode = "rgmii-id";
		rx-clk-delay = <0x4000>; /* for RGMII */
		tx-clk-delay = <0x1f>; /* for RGMII */

		phy-handle = <&phy_88E1111>;
		mdio0 {
			#address-cells = <1>;
			#size-cells = <0>;
			compatible = "snps,dwmac-mdio";

			phy_88E1111: ethernet-phy@0 {
				reg = <0x1>;
			};
		};
	};
