ARM: dts: stm32: Add alternate pinmux for USART2 pins on stm32mp15

Add mux option for USART2 pins, this is used on AV96 board.
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Alexandre Torgue <alexandre.torgue@st.com>
Cc: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Cc: linux-stm32@st-md-mailman.stormreply.com
To: linux-arm-kernel@lists.infradead.org
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32mp15-pinctrl.dtsi

@@ -1389,6 +1389,30 @@ pins {
 		};
 	};
 
+	usart2_pins_a: usart2-0 {
+		pins1 {
+			pinmux = <STM32_PINMUX('F', 5, AF7)>, /* USART2_TX */
+				 <STM32_PINMUX('D', 4, AF7)>; /* USART2_RTS */
+			bias-disable;
+			drive-push-pull;
+			slew-rate = <0>;
+		};
+		pins2 {
+			pinmux = <STM32_PINMUX('D', 6, AF7)>, /* USART2_RX */
+				 <STM32_PINMUX('D', 3, AF7)>; /* USART2_CTS_NSS */
+			bias-disable;
+		};
+	};
+
+	usart2_sleep_pins_a: usart2-sleep-0 {
+		pins {
+			pinmux = <STM32_PINMUX('F', 5, ANALOG)>, /* USART2_TX */
+				 <STM32_PINMUX('D', 4, ANALOG)>, /* USART2_RTS */
+				 <STM32_PINMUX('D', 6, ANALOG)>, /* USART2_RX */
+				 <STM32_PINMUX('D', 3, ANALOG)>; /* USART2_CTS_NSS */
+		};
+	};
+
 	usart3_pins_a: usart3-0 {
 		pins1 {
 			pinmux = <STM32_PINMUX('B', 10, AF7)>; /* USART3_TX */