ARM: dts: stm32: add pin map for i2c3 controller on stm32f7

Add pin configurations for using i2c3 controller on stm32f7.
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm/boot/dts/st/stm32f7-pinctrl.dtsi

@@ -171,6 +171,16 @@ pins {
 				};
 			};
 
+			i2c3_pins_a: i2c3-0 {
+				pins {
+					pinmux = <STM32_PINMUX('H', 8, AF4)>, /* I2C3_SDA */
+						 <STM32_PINMUX('H', 7, AF4)>; /* I2C3_SCL */
+					bias-disable;
+					drive-open-drain;
+					slew-rate = <0>;
+				};
+			};
+
 			usbotg_hs_pins_a: usbotg-hs-0 {
 				pins {
 					pinmux = <STM32_PINMUX('H', 4, AF10)>, /* OTG_HS_ULPI_NXT */