dt-bindings: power: supply: gpio-charger: convert to yaml

Convert the gpio-charger bindings from text format to
new YAML based representation.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

Documentation/devicetree/bindings/power/supply/gpio-charger.txt

-gpio-charger
-
-Required properties :
- - compatible : "gpio-charger"
- - gpios : GPIO indicating the charger presence.
-   See GPIO binding in bindings/gpio/gpio.txt .
- - charger-type : power supply type, one of
-     unknown
-     battery
-     ups
-     mains
-     usb-sdp (USB standard downstream port)
-     usb-dcp (USB dedicated charging port)
-     usb-cdp (USB charging downstream port)
-     usb-aca (USB accessory charger adapter)
-
-Optional properties:
- - charge-status-gpios: GPIO indicating whether a battery is charging.
-
-Example:
-
-	usb_charger: charger {
-		compatible = "gpio-charger";
-		charger-type = "usb-sdp";
-		gpios = <&gpd 28 GPIO_ACTIVE_LOW>;
-		charge-status-gpios = <&gpc 27 GPIO_ACTIVE_LOW>;
-	};
-
-	battery {
-		power-supplies = <&usb_charger>;
-	};

Documentation/devicetree/bindings/power/supply/gpio-charger.yaml

+# SPDX-License-Identifier: GPL-2.0
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/power/supply/gpio-charger.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: simple battery chargers only communicating through GPIOs
+
+maintainers:
+  - Sebastian Reichel <sre@kernel.org>
+
+description:
+  This binding is for all chargers, which are working more or less
+  autonomously, only providing some status GPIOs and possibly some
+  GPIOs for limited control over the charging process.
+
+properties:
+  compatible:
+    const: gpio-charger
+
+  charger-type:
+    enum:
+      - unknown
+      - battery
+      - ups
+      - mains
+      - usb-sdp                   # USB standard downstream port
+      - usb-dcp                   # USB dedicated charging port
+      - usb-cdp                   # USB charging downstream port
+      - usb-aca                   # USB accessory charger adapter
+    description:
+      Type of the charger, e.g. "mains" for a wall charger.
+
+  gpios:
+    maxItems: 1
+    description: GPIO indicating the charger presence
+
+  charge-status-gpios:
+    maxItems: 1
+    description: GPIO indicating the charging status
+
+required:
+  - compatible
+  - gpios
+
+additionalProperties: false
+
+examples:
+  - |
+    #include <dt-bindings/gpio/gpio.h>
+
+    charger {
+      compatible = "gpio-charger";
+      charger-type = "usb-sdp";
+
+      gpios = <&gpd 28 GPIO_ACTIVE_LOW>;
+      charge-status-gpios = <&gpc 27 GPIO_ACTIVE_LOW>;
+    };