ARM: dts: imx6q-tbs2910: Add an mdio node

imx6q-tbs2910 has an Atheros AR8035 Ethernet PHY at address 4.

The AR8035 provides a 125MHz clock to the ENET_REF_CLK i.MX6 pin.

Improve the Ethernet representation by adding an mdio node with such
information.

This fixes an Ethernet regression in U-Boot as U-Boot AR803X driver now
expects the 'qca,clk-out-frequency' property to be passed via
device tree.
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Reviewed-by: Soeren Moch <smoch@web.de>
Tested-by: Soeren Moch <smoch@web.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6q-tbs2910.dts

@@ -100,7 +100,18 @@ &fec {
 	pinctrl-0 = <&pinctrl_enet>;
 	phy-mode = "rgmii-id";
 	phy-reset-gpios = <&gpio1 25 GPIO_ACTIVE_LOW>;
+	phy-handle = <&phy>;
 	status = "okay";
+
+	mdio {
+		#address-cells = <1>;
+		#size-cells = <0>;
+
+		phy: ethernet-phy@4 {
+			reg = <4>;
+			qca,clk-out-frequency = <125000000>;
+		};
+	};
 };
 
 &hdmi {