ARM: dts: stm32: Add TIMERS inverted PWM channel 3 on STM32MP135F-DK

The pwm source TIM1_CH3N channel (on PE12) in inverted polarity mode
will be used to manage the brightness of the panel backlight on
STM32MP135F-DK.

Signed-off-by: Cheick Traore <cheick.traore@foss.st.com>
Reviewed-by: Fabrice Gasnier <fabrice.gasnier@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/arch/arm/dts/stm32mp13-pinctrl.dtsi b/arch/arm/dts/stm32mp13-pinctrl.dtsi
index c01d39f..52c2a9f 100644
--- a/arch/arm/dts/stm32mp13-pinctrl.dtsi
+++ b/arch/arm/dts/stm32mp13-pinctrl.dtsi
@@ -215,6 +215,21 @@
 		};
 	};
 
+	pwm1_ch3n_pins_a: pwm1-ch3n-0 {
+		pins {
+			pinmux = <STM32_PINMUX('E', 12, AF1)>; /* TIM1_CH3N */
+			bias-pull-down;
+			drive-push-pull;
+			slew-rate = <0>;
+		};
+	};
+
+	pwm1_ch3n_sleep_pins_a: pwm1-ch3n-sleep-0 {
+		pins {
+			pinmux = <STM32_PINMUX('E', 12, ANALOG)>; /* TIM1_CH3N */
+		};
+	};
+
 	pwm3_pins_a: pwm3-0 {
 		pins {
 			pinmux = <STM32_PINMUX('B', 1, AF2)>; /* TIM3_CH4 */