ARM: DT: stm32f7: add ethernet pin contol node

It also removes the ethernet pin configuration done during the board
initialization.

Signed-off-by: Vikas Manocha <vikas.manocha@st.com>
diff --git a/arch/arm/dts/stm32f746-disco.dts b/arch/arm/dts/stm32f746-disco.dts
index 6734f23..3d6002f 100644
--- a/arch/arm/dts/stm32f746-disco.dts
+++ b/arch/arm/dts/stm32f746-disco.dts
@@ -78,6 +78,7 @@
 
 &mac {
 	status = "okay";
+	pinctrl-0 = <&ethernet_mii>;
 	phy-mode = "rmii";
 	phy-handle = <&phy0>;