Altera SOCFPGA SoC DWMAC controller

This is a variant of the dwmac/stmmac driver an inherits all descriptions
present in Documentation/devicetree/bindings/net/stmmac.txt.

The device node has additional properties:

Required properties:
 - compatible	: Should contain "altr,socfpga-stmmac" along with
		  "snps,dwmac" and any applicable more detailed
		  designware version numbers documented in stmmac.txt
 - altr,sysmgr-syscon : Should be the phandle to the system manager node that
   encompasses the glue register, the register offset, and the register shift.
 - altr,f2h_ptp_ref_clk use f2h_ptp_ref_clk instead of default eosc1 clock
   for ptp ref clk. This affects all emacs as the clock is common.

Optional properties:
altr,emac-splitter: Should be the phandle to the emac splitter soft IP node if
		DWMAC controller is connected emac splitter.

Example:

gmac0: ethernet@ff700000 {
	compatible = "altr,socfpga-stmmac", "snps,dwmac-3.70a", "snps,dwmac";
	altr,sysmgr-syscon = <&sysmgr 0x60 0>;
	status = "disabled";
	reg = <0xff700000 0x2000>;
	interrupts = <0 115 4>;
	interrupt-names = "macirq";
	mac-address = [00 00 00 00 00 00];/* Filled in by U-Boot */
	clocks = <&emac_0_clk>;
	clock-names = "stmmaceth";
};