ARM: dts: stm32: Add pin map for I2C3 controller on stm32f4

This patch adds the pin configuration for I2C3 controller on
stm32f4.
Signed-off-by: dillon min <dillon.minfei@gmail.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32f4-pinctrl.dtsi

@@ -383,6 +383,18 @@ pins2 {
 				};
 			};
 
+			i2c3_pins: i2c3-0 {
+				pins {
+					pinmux = <STM32_PINMUX('C', 9, AF4)>,
+						/* I2C3_SDA */
+						 <STM32_PINMUX('A', 8, AF4)>;
+						/* I2C3_SCL */
+					bias-disable;
+					drive-open-drain;
+					slew-rate = <3>;
+				};
+			};
+
 			dcmi_pins: dcmi-0 {
 				pins {
 					pinmux = <STM32_PINMUX('A', 4, AF13)>, /* DCMI_HSYNC */