dt-bindings: leds: Add binding for sgm3140

Add YAML devicetree binding for SGMICRO SGM3140 charge pump used for
camera flash LEDs.

Signed-off-by: Luca Weiss <luca@z3ntu.xyz>
Reviewed-by: Dan Murphy <dmurphy@ti.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>

Documentation/devicetree/bindings/leds/leds-sgm3140.yaml

+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/leds/leds-sgm3140.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: SGMICRO SGM3140 500mA Buck/Boost Charge Pump LED Driver
+
+maintainers:
+  - Luca Weiss <luca@z3ntu.xyz>
+
+description: |
+  The SGM3140 is a current-regulated charge pump which can regulate two current
+  levels for Flash and Torch modes.
+
+  The data sheet can be found at:
+    http://www.sg-micro.com/uploads/soft/20190626/1561535688.pdf
+
+properties:
+  compatible:
+    const: sgmicro,sgm3140
+
+  enable-gpios:
+    maxItems: 1
+    description: A connection to the 'EN' pin.
+
+  flash-gpios:
+    maxItems: 1
+    description: A connection to the 'FLASH' pin.
+
+  vin-supply:
+    description: Regulator providing power to the 'VIN' pin.
+
+  led:
+    type: object
+    allOf:
+      - $ref: common.yaml#
+
+required:
+  - compatible
+  - flash-gpios
+  - enable-gpios
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+    #include <dt-bindings/leds/common.h>
+
+    led-controller {
+        compatible = "sgmicro,sgm3140";
+        flash-gpios = <&pio 3 24 GPIO_ACTIVE_HIGH>; /* PD24 */
+        enable-gpios = <&pio 2 3 GPIO_ACTIVE_HIGH>; /* PC3 */
+        vin-supply = <&reg_dcdc1>;
+
+        sgm3140_flash: led {
+            function = LED_FUNCTION_FLASH;
+            color = <LED_COLOR_ID_WHITE>;
+            flash-max-timeout-us = <250000>;
+        };
+    };