ARM: DT: stm32f7: add pin control node for serial port pins

And remove the uart pin configuration from 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 454b515..6734f23 100644
--- a/arch/arm/dts/stm32f746-disco.dts
+++ b/arch/arm/dts/stm32f746-disco.dts
@@ -70,6 +70,12 @@
 	clock-frequency = <25000000>;
 };
 
+&usart1 {
+	pinctrl-0 = <&usart1_pins_a>;
+	pinctrl-names = "default";
+	status = "okay";
+};
+
 &mac {
 	status = "okay";
 	phy-mode = "rmii";
diff --git a/arch/arm/dts/stm32f746.dtsi b/arch/arm/dts/stm32f746.dtsi
index f59eca8..867f399 100644
--- a/arch/arm/dts/stm32f746.dtsi
+++ b/arch/arm/dts/stm32f746.dtsi
@@ -104,6 +104,19 @@
 			ranges = <0 0x40020000 0x3000>;
 			u-boot,dm-pre-reloc;
 			pins-are-numbered;
+
+			usart1_pins_a: usart1@0 {
+				pins1 {
+					pinmux = <STM32F746_PA9_FUNC_USART1_TX>;
+					bias-disable;
+					drive-push-pull;
+					slew-rate = <2>;
+				};
+				pins2 {
+					pinmux = <STM32F746_PB7_FUNC_USART1_RX>;
+					bias-disable;
+				};
+			};
 		};
 	};
 };