dt-bindings: leds: add Broadcom's BCM63138 controller

Broadcom used 2 LEDs hardware blocks for their BCM63xx SoCs:
1. Older one (BCM6318, BCM6328, BCM6362, BCM63268, BCM6838)
2. Newer one (BCM6848, BCM6858, BCM63138, BCM63148, BCM63381, BCM68360)

The newer one was also later also used on BCM4908 SoC.

Old block is already documented in the leds-bcm6328.yaml. This binding
documents the new one which uses different registers & programming. It's
first used in BCM63138 thus the binding name.
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

Documentation/devicetree/bindings/leds/leds-bcm63138.yaml

+# SPDX-License-Identifier: GPL-2.0-only OR BSD-2-Clause
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/leds-bcm63138.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Broadcom's BCM63138 LEDs controller
+
+maintainers:
+  - Rafał Miłecki <rafal@milecki.pl>
+
+description: |
+  This LEDs controller was first used on BCM63138 and later reused on BCM4908,
+  BCM6848, BCM6858, BCM63138, BCM63148, BCM63381 and BCM68360 SoCs.
+
+  It supports up to 32 LEDs that can be connected parallelly or serially. It
+  also includes limited support for hardware blinking.
+
+  Binding serially connected LEDs isn't documented yet.
+
+properties:
+  compatible:
+    oneOf:
+      - items:
+          - enum:
+              - brcm,bcm4908-leds
+              - brcm,bcm6848-leds
+              - brcm,bcm6858-leds
+              - brcm,bcm63148-leds
+              - brcm,bcm63381-leds
+              - brcm,bcm68360-leds
+          - const: brcm,bcm63138-leds
+      - const: brcm,bcm63138-leds
+
+  reg:
+    maxItems: 1
+
+  "#address-cells":
+    const: 1
+
+  "#size-cells":
+    const: 0
+
+patternProperties:
+  "^led@[a-f0-9]+$":
+    type: object
+
+    $ref: common.yaml#
+
+    properties:
+      reg:
+        maxItems: 1
+        description: LED pin number
+
+      active-low:
+        type: boolean
+        description: Makes LED active low.
+
+    required:
+      - reg
+
+    unevaluatedProperties: false
+
+required:
+  - reg
+  - "#address-cells"
+  - "#size-cells"
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/leds/common.h>
+
+    leds@ff800800 {
+        compatible = "brcm,bcm4908-leds", "brcm,bcm63138-leds";
+        reg = <0xff800800 0xdc>;
+
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        led@0 {
+            reg = <0x0>;
+            function = LED_FUNCTION_POWER;
+            color = <LED_COLOR_ID_GREEN>;
+            default-state = "on";
+        };
+
+        led@3 {
+            reg = <0x3>;
+            function = LED_FUNCTION_STATUS;
+            color = <LED_COLOR_ID_GREEN>;
+            active-low;
+        };
+    };