dt-bindings: leds: Add binding for a multicolor group of LEDs

This allows to group multiple monochromatic LEDs into a multicolor
LED, e.g. RGB LEDs.
Signed-off-by: Jean-Jacques Hiblot <jjhiblot@traphandler.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230728153731.3742339-4-jjhiblot@traphandler.comSigned-off-by: Lee Jones <lee@kernel.org>

Documentation/devicetree/bindings/leds/leds-group-multicolor.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/leds-group-multicolor.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Multi-color LED built with monochromatic LEDs
+
+maintainers:
+  - Jean-Jacques Hiblot <jjhiblot@traphandler.com>
+
+description: |
+  This driver combines several monochromatic LEDs into one multi-color
+  LED using the multicolor LED class.
+
+properties:
+  compatible:
+    const: leds-group-multicolor
+
+  leds:
+    description:
+      An aray of monochromatic leds
+    $ref: /schemas/types.yaml#/definitions/phandle-array
+
+required:
+  - leds
+
+allOf:
+  - $ref: leds-class-multicolor.yaml#
+
+unevaluatedProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/leds/common.h>
+
+    monochromatic-leds {
+        compatible = "gpio-leds";
+
+        led0: led-0 {
+            gpios = <&mcu_pio 0 GPIO_ACTIVE_LOW>;
+            color = <LED_COLOR_ID_RED>;
+        };
+
+        led1: led-1 {
+            gpios = <&mcu_pio 1 GPIO_ACTIVE_HIGH>;
+            color = <LED_COLOR_ID_GREEN>;
+        };
+
+        led2: led-2 {
+            gpios = <&mcu_pio 2 GPIO_ACTIVE_HIGH>;
+            color = <LED_COLOR_ID_BLUE>;
+        };
+    };
+
+    multi-led {
+        compatible = "leds-group-multicolor";
+        color = <LED_COLOR_ID_RGB>;
+        function = LED_FUNCTION_INDICATOR;
+        leds = <&led0>, <&led1>, <&led2>;
+    };
+
+...