ARM: dts: exynos: Specify snps, dwmac in compatible string for gmac

devicetree binding for stmmac states:
- compatible: Should be "snps,dwmac-<ip_version>", "snps,dwmac"
	For backwards compatibility: "st,spear600-gmac" is also supported.

No functional change intended.
Signed-off-by: NNiklas Cassel <niklas.cassel@axis.com>
Signed-off-by: NKrzysztof Kozlowski <krzk@kernel.org>

arch/arm/boot/dts/exynos5440.dtsi

@@ -188,7 +188,7 @@
 	};
 
 	gmac: ethernet@00230000 {
-		compatible = "snps,dwmac-3.70a";
+		compatible = "snps,dwmac-3.70a", "snps,dwmac";
 		reg = <0x00230000 0x8000>;
 		interrupt-parent = <&gic>;
 		interrupts = <0 31 4>;