ARM: dts: stm32: Add missing USART3 pin config to stm32f469-disco board

This patch adds USART3 pin configuration on PB10/PA11 pins
for STM32F469I-DISCO board.
Signed-off-by: Bruno Herrera <bruherrera@gmail.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32f429.dtsi

@@ -316,6 +316,19 @@ pins2 {
 				};
 			};
 
+			usart3_pins_a: usart3@0 {
+				pins1 {
+					pinmux = <STM32F429_PB10_FUNC_USART3_TX>;
+					bias-disable;
+					drive-push-pull;
+					slew-rate = <0>;
+				};
+				pins2 {
+					pinmux = <STM32F429_PB11_FUNC_USART3_RX>;
+					bias-disable;
+				};
+			};
+
 			usbotg_hs_pins_a: usbotg_hs@0 {
 				pins {
 					pinmux = <STM32F429_PH4_FUNC_OTG_HS_ULPI_NXT>,

arch/arm/boot/dts/stm32f469-disco.dts

@@ -79,5 +79,7 @@ &clk_hse {
 };
 
 &usart3 {
+	pinctrl-0 = <&usart3_pins_a>;
+	pinctrl-names = "default";
 	status = "okay";
 };