ARM: dts: imx6dl-riotboard: properly define rgmii PHY

The Atheros AR8035 PHY can be autodetected but can't use interrupt
support provided on this board. Define MDIO bus and the PHY node to make
it work properly.
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6dl-riotboard.dts

@@ -89,11 +89,25 @@ &fec {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_enet>;
 	phy-mode = "rgmii-id";
-	phy-reset-gpios = <&gpio3 31 GPIO_ACTIVE_LOW>;
+	phy-handle = <&rgmii_phy>;
 	interrupts-extended = <&gpio1 6 IRQ_TYPE_LEVEL_HIGH>,
 			      <&intc 0 119 IRQ_TYPE_LEVEL_HIGH>;
 	fsl,err006687-workaround-present;
 	status = "okay";
+
+	mdio {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		/* Atheros AR8035 PHY */
+		rgmii_phy: ethernet-phy@4 {
+			reg = <4>;
+			interrupts-extended = <&gpio1 28 IRQ_TYPE_LEVEL_LOW>;
+			reset-gpios = <&gpio3 31 GPIO_ACTIVE_LOW>;
+			reset-assert-us = <10000>;
+			reset-deassert-us = <1000>;
+		};
+	};
 };
 
 &gpio1 {