arm64: allwinner: pine64-plus: Enable dwmac-sun8i

The dwmac-sun8i hardware is present on the pine64 plus.
It uses an external PHY rtl8211e via RGMII.

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

arch/arm64/boot/dts/allwinner/sun50i-a64-pine64-plus.dts

@@ -46,5 +46,20 @@
 	model = "Pine64+";
 	compatible = "pine64,pine64-plus", "allwinner,sun50i-a64";
 
-	/* TODO: Camera, Ethernet PHY, touchscreen, etc. */
+	/* TODO: Camera, touchscreen, etc. */
+};
+
+&emac {
+	pinctrl-names = "default";
+	pinctrl-0 = <&rgmii_pins>;
+	phy-mode = "rgmii";
+	phy-handle = <&ext_rgmii_phy>;
+	status = "okay";
+};
+
+&mdio {
+	ext_rgmii_phy: ethernet-phy@1 {
+		compatible = "ethernet-phy-ieee802.3-c22";
+		reg = <1>;
+	};
 };