feat(stm32mp2-fdts): add stm32mp257f-ev1 board

Add STM32MP257F Evaluation board support. It embeds a STM32MP257FAI
SoC, with 4GB of DDR4, TSN switch (2+1 ports), 2*USB typeA, 1*USB2
typeC, SNOR OctoSPI, mini PCIe, STPMIC2 for power distribution ...

Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I92da3a7085a4d2f2d606777c4215aed55f77c589
diff --git a/fdts/stm32mp25-pinctrl.dtsi b/fdts/stm32mp25-pinctrl.dtsi
index 4147449..8d0eaaf 100644
--- a/fdts/stm32mp25-pinctrl.dtsi
+++ b/fdts/stm32mp25-pinctrl.dtsi
@@ -4,3 +4,18 @@
  * Author: Alexandre Torgue <alexandre.torgue@foss.st.com> for STMicroelectronics.
  */
 #include <dt-bindings/pinctrl/stm32-pinfunc.h>
+
+&pinctrl {
+	usart2_pins_a: usart2-0 {
+		pins1 {
+			pinmux = <STM32_PINMUX('A', 4, AF6)>; /* USART2_TX */
+			bias-disable;
+			drive-push-pull;
+			slew-rate = <0>;
+		};
+		pins2 {
+			pinmux = <STM32_PINMUX('A', 8, AF8)>; /* USART2_RX */
+			bias-disable;
+		};
+	};
+};