dt-bindings: net: Document bindings for anarion-gmac

Signed-off-by: NAlexandru Gagniuc <alex.g@adaptrum.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/anarion-gmac.txt

+*  Adaptrum Anarion ethernet controller
+
+This device is a platform glue layer for stmmac.
+Please see stmmac.txt for the other unchanged properties.
+
+Required properties:
+ - compatible:  Should be "adaptrum,anarion-gmac", "snps,dwmac"
+ - phy-mode:    Should be "rgmii". Other modes are not currently supported.
+
+
+Examples:
+
+	gmac1: ethernet@f2014000 {
+		compatible = "adaptrum,anarion-gmac", "snps,dwmac";
+		reg = <0xf2014000 0x4000>, <0xf2018100 8>;
+
+		interrupt-parent = <&core_intc>;
+		interrupts = <21>;
+		interrupt-names = "macirq";
+
+		clocks = <&core_clk>;
+		clock-names = "stmmaceth";
+
+		phy-mode = "rgmii";
+	};