dt-bindings: backlight: Add Kinetic KTD253 bindings

This adds device tree bindings for the Kinetic KTD253
white LED backlight driver.

Cc: devicetree@vger.kernel.org
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/leds/backlight/kinetic,ktd253.yaml

+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/backlight/kinetic,ktd253.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Kinetic Technologies KTD253 one-wire backlight
+
+maintainers:
+  - Linus Walleij <linus.walleij@linaro.org>
+
+description: |
+  The Kinetic Technologies KTD253 is a white LED backlight that is
+  controlled by a single GPIO line. If you just turn on the backlight
+  it goes to maximum backlight then you can set the level of backlight
+  using pulses on the enable wire. This is sometimes referred to as
+  "expresswire".
+
+allOf:
+  - $ref: common.yaml#
+
+properties:
+  compatible:
+    const: kinetic,ktd253
+
+  enable-gpios:
+    description: GPIO to use to enable/disable and dim the backlight.
+    maxItems: 1
+
+  default-brightness: true
+  max-brightness: true
+
+required:
+  - compatible
+  - enable-gpios
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    backlight {
+        compatible = "kinetic,ktd253";
+        enable-gpios = <&gpio2 5 GPIO_ACTIVE_HIGH>;
+        default-brightness = <13>;
+    };