dt-bindings: leds: Add multicolor PWM LED bindings

This allows to group multiple PWM-connected monochrome LEDs into
multicolor LEDs, e.g. RGB LEDs.
Signed-off-by: Sven Schwermer <sven.schwermer@disruptive-technologies.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

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

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/leds-pwm-multicolor.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Multi-color LEDs connected to PWM
+
+maintainers:
+  - Sven Schwermer <sven.schwermer@disruptive-technologies.com>
+
+description: |
+  This driver combines several monochrome PWM LEDs into one multi-color
+  LED using the multicolor LED class.
+
+properties:
+  compatible:
+    const: pwm-leds-multicolor
+
+  multi-led:
+    type: object
+
+    patternProperties:
+      "^led-[0-9a-z]+$":
+        type: object
+        $ref: common.yaml#
+
+        additionalProperties: false
+
+        properties:
+          pwms:
+            maxItems: 1
+
+          pwm-names: true
+
+          color: true
+
+        required:
+          - pwms
+          - color
+
+required:
+  - compatible
+
+allOf:
+  - $ref: leds-class-multicolor.yaml#
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/leds/common.h>
+
+    led-controller {
+        compatible = "pwm-leds-multicolor";
+
+        multi-led {
+          color = <LED_COLOR_ID_RGB>;
+          function = LED_FUNCTION_INDICATOR;
+          max-brightness = <65535>;
+
+          led-red {
+              pwms = <&pwm1 0 1000000>;
+              color = <LED_COLOR_ID_RED>;
+          };
+
+          led-green {
+              pwms = <&pwm2 0 1000000>;
+              color = <LED_COLOR_ID_GREEN>;
+          };
+
+          led-blue {
+              pwms = <&pwm3 0 1000000>;
+              color = <LED_COLOR_ID_BLUE>;
+          };
+        };
+    };
+
+...