dt: bindings: Add multicolor class dt bindings documention

Add DT bindings for the LEDs multicolor class framework.
Add multicolor ID to the color ID list for device tree bindings.

CC: Rob Herring <robh@kernel.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Signed-off-by: Dan Murphy <dmurphy@ti.com>
Reviewed-by: Marek Behún <marek.behun@nic.cz>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

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

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/leds-class-multicolor.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Common properties for the multicolor LED class.
+
+maintainers:
+  - Dan Murphy <dmurphy@ti.com>
+
+description: |
+  Bindings for multi color LEDs show how to describe current outputs of
+  either integrated multi-color LED elements (like RGB, RGBW, RGBWA-UV
+  etc.) or standalone LEDs, to achieve logically grouped multi-color LED
+  modules. This is achieved by adding multi-led nodes layer to the
+  monochrome LED bindings.
+  The nodes and properties defined in this document are unique to the multicolor
+  LED class.  Common LED nodes and properties are inherited from the common.txt
+  within this documentation directory.
+
+patternProperties:
+  "^multi-led@([0-9a-f])$":
+    type: object
+    description: Represents the LEDs that are to be grouped.
+    properties:
+      color:
+        const: 8  # LED_COLOR_ID_MULTI
+        description: |
+          For multicolor LED support this property should be defined as
+          LED_COLOR_ID_MULTI which can be found in include/linux/leds/common.h.
+
+    $ref: "common.yaml#"
+
+    required:
+      - color
+...

include/dt-bindings/leds/common.h

@@ -30,7 +30,8 @@
 #define LED_COLOR_ID_VIOLET	5
 #define LED_COLOR_ID_YELLOW	6
 #define LED_COLOR_ID_IR		7
-#define LED_COLOR_ID_MAX	8
+#define LED_COLOR_ID_MULTI	8
+#define LED_COLOR_ID_MAX	9
 
 /* Standard LED functions */
 /* Keyboard LEDs, usually it would be input4::capslock etc. */