ARM: dts: imx6q-prtwd2: configure ethernet reference clock parent

On this board the PHY is the ref clock provider. So, configure ethernet
reference clock as input.
Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm/boot/dts/imx6q-prtwd2.dts

@@ -22,6 +22,13 @@ memory@80000000 {
 		reg = <0x80000000 0x20000000>;
 	};
 
+	clk50m_phy: phy-clock {
+		compatible = "fixed-clock";
+		#clock-cells = <0>;
+		clock-frequency = <50000000>;
+		clock-output-names = "enet_ref_pad";
+	};
+
 	usdhc2_wifi_pwrseq: usdhc2_wifi_pwrseq {
 		compatible = "mmc-pwrseq-simple";
 		pinctrl-names = "default";
@@ -49,13 +56,17 @@ &can1 {
 	status = "okay";
 };
 
+&clks {
+	clocks = <&clk50m_phy>;
+	clock-names = "enet_ref_pad";
+	assigned-clocks = <&clks IMX6QDL_CLK_ENET_REF_SEL>;
+	assigned-clock-parents = <&clk50m_phy>;
+};
+
 &fec {
 	pinctrl-names = "default";
 	pinctrl-0 = <&pinctrl_enet>;
 	phy-mode = "rmii";
-	clocks = <&clks IMX6QDL_CLK_ENET>,
-		 <&clks IMX6QDL_CLK_ENET>;
-	clock-names = "ipg", "ahb";
 	status = "okay";
 
 	fixed-link {