dts: bindings: led: introduce leds-group-multicolor binding

The leds-group-multicolor binding allows to combines several
monochromatic LEDs into one multi-color LED.

Signed-off-by: Simon Guinot <simon.guinot@seagate.com>

dts/bindings/led/leds-group-multicolor.yaml

@@ -0,0 +1,49 @@
+# Copyright (c) 2025 Seagate Technology LLC
+# SPDX-License-Identifier: Apache-2.0
+
+title: Combines several monochromatic LEDs into one multi-color LED.
+
+description: |
+  Here is an example that defines an RGB LED with a group of monochromatic
+  PWM LEDs. Note that the pwms property definition handle depends on the PWM
+  controller model. In this example, an STM32 PWM controller is assumed.
+
+  #include <zephyr/dt-bindings/led/led.h>
+
+  / {
+          monochromatic-leds {
+                  compatible = "pwm-leds";
+
+                  red_pwm_led: led-0 {
+                          pwms = <&pwm1 1 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
+                  };
+
+                  green_pwm_led: led-1 {
+                          pwms = <&pwm2 1 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
+                  };
+
+                  blue_pwm_led: led-2 {
+                          pwms = <&pwm3 1 PWM_MSEC(20) PWM_POLARITY_NORMAL>;
+                  };
+          };
+
+          rgb-led {
+                  compatible = "leds-group-multicolor";
+
+                  leds = <&red_pwm_led>, <&green_pwm_led>, <&blue_pwm_led>;
+                  color-mapping = <LED_COLOR_ID_RED>,
+                                  <LED_COLOR_ID_GREEN>,
+                                  <LED_COLOR_ID_BLUE>;
+          };
+  };
+
+compatible: "leds-group-multicolor"
+
+include: led-node.yaml
+
+properties:
+  leds:
+    required: true
+    type: phandles
+    description: |
+      References to monochromatic LED nodes.