ARM: dts: stm32: add blue led (Linux heartbeat) on stm32mp135f-dk

The blue led (Linux heartbeat) is connected to the PA14 pin of the
stm32mp135f-dk board.
Signed-off-by: Fabien Dessenne <fabien.dessenne@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>

arch/arm/boot/dts/stm32mp135f-dk.dts

@@ -6,6 +6,8 @@
 
 /dts-v1/;
 
+#include <dt-bindings/gpio/gpio.h>
+#include <dt-bindings/leds/common.h>
 #include "stm32mp135.dtsi"
 #include "stm32mp13xf.dtsi"
 #include "stm32mp13-pinctrl.dtsi"
@@ -23,6 +25,18 @@ memory@c0000000 {
 		reg = <0xc0000000 0x20000000>;
 	};
 
+	leds {
+		compatible = "gpio-leds";
+
+		led-blue {
+			function = LED_FUNCTION_HEARTBEAT;
+			color = <LED_COLOR_ID_BLUE>;
+			gpios = <&gpioa 14 GPIO_ACTIVE_LOW>;
+			linux,default-trigger = "heartbeat";
+			default-state = "off";
+		};
+	};
+
 	vdd_sd: vdd-sd {
 		compatible = "regulator-fixed";
 		regulator-name = "vdd_sd";