leds: rt4505: Add DT binding document for Richtek RT4505

Add DT binding document for Richtek RT4505 flash LED controller.
Signed-off-by: NChiYuan Huang <cy_huang@richtek.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Signed-off-by: NPavel Machek <pavel@ucw.cz>

Documentation/devicetree/bindings/leds/leds-rt4505.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/leds-rt4505.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Richtek RT4505 Single Channel LED Driver
+
+maintainers:
+  - ChiYuan Huang <cy_huang@richtek.com>
+
+description: |
+  The RT4505 is a flash LED driver that can support up to 375mA and 1.5A for
+  torch and flash mode, respectively.
+
+  The data sheet can be found at:
+    https://www.richtek.com/assets/product_file/RT4505/DS4505-02.pdf
+
+properties:
+  compatible:
+    const: richtek,rt4505
+
+  reg:
+    description: I2C slave address of the controller.
+    maxItems: 1
+
+  led:
+    type: object
+    $ref: common.yaml#
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/leds/common.h>
+
+    i2c0 {
+      #address-cells = <1>;
+      #size-cells = <0>;
+
+      led-controller@63 {
+        compatible = "richtek,rt4505";
+        reg = <0x63>;
+
+        rt4505_flash: led {
+          function = LED_FUNCTION_FLASH;
+          color = <LED_COLOR_ID_WHITE>;
+          led-max-microamp = <375000>;
+          flash-max-microamp = <1500000>;
+          flash-max-timeout-us = <800000>;
+        };
+      };
+    };