ARM: dts: sun6i: Add ethernet alias for GMAC

Alias GMAC as ethernet0 so U-boot can fill in the MAC address.
Signed-off-by: NChen-Yu Tsai <wens@csie.org>
Signed-off-by: NMaxime Ripard <maxime.ripard@free-electrons.com>

arch/arm/boot/dts/sun6i-a31.dtsi

@@ -23,6 +23,7 @@
 		serial3 = &uart3;
 		serial4 = &uart4;
 		serial5 = &uart5;
+		ethernet0 = &gmac;
 	};