STMicroelectronics SoC DWMAC controller

The device node has following properties.

Required properties:
 - compatible	: Can be "st,stih415-dwmac", "st,stih416-dwmac" or
   "st,stid127-dwmac".
 - reg		: Offset of the glue configuration register map in system
   configuration regmap pointed by st,syscon property and size.
 - st,syscon	: Should be phandle to system configuration node which
   encompases this glue registers.
 - st,gmac_en: this is to enable the gmac into a dedicated sysctl control
   register available on STiH407 SoC.

Optional properties:
 - resets	: phandle pointing to the system reset controller with correct
   reset line index for ethernet reset.
 - st,ext-phyclk: valid only for RMII where PHY can generate 50MHz clock or
   MAC can generate it.
 - st,tx-retime-src: This specifies which clk is wired up to the mac for
   retimeing tx lines. This is totally board dependent and can take one of the
   posssible values from "txclk", "clk_125" or "clkgen".
   If not passed, the internal clock will be used by default.

Sub-nodes:
The dwmac core should be added as subnode to STMicroelectronics dwmac glue.
- dwmac :	The binding details of dwmac can be found in
  Documentation/devicetree/bindings/net/stmmac.txt

Example:

ethernet0: ethernet0{
	#address-cells = <1>;
	#size-cells = <1>;
	compatible		= "st,stih415-dwmac";
	reg			= <0x148 0x4>;
	resets			= <&softreset STIH415_ETH0_SOFTRESET>;
	st,syscon		= <&syscfg_rear>;
	st,tx-retime-src	= "clk_125";
	ranges;

	dwmac0:dwmac@fe810000 {
		device_type 	= "network";
		compatible	= "snps,dwmac", "snps,dwmac-3.610";
		reg 		= <0xfe810000 0x8000>;
		interrupts 	= <0 147 0>;
		interrupt-names = "macirq";
		...
	};
};
