ARM64: dts: meson-axg: enable ethernet for A113D S400 board

This is tested in the S400 dev board which use a RTL8211F PHY,
and the pins connect to the 'eth_rgmii_y_pins' group.
Reviewed-by: NNeil Armstrong <narmstrong@baylibre.com>
Signed-off-by: NYixun Lan <yixun.lan@amlogic.com>
Signed-off-by: NKevin Hilman <khilman@baylibre.com>

arch/arm64/boot/dts/amlogic/meson-axg-s400.dts

@@ -17,6 +17,13 @@
 	};
 };
 
+&ethmac {
+	status = "okay";
+	phy-mode = "rgmii";
+	pinctrl-0 = <&eth_rgmii_y_pins>;
+	pinctrl-names = "default";
+};
+
 &uart_AO {
 	status = "okay";
 };