power: add documentation for ACT8945A's charger DT bindings

This patch adds documentation for the DT bindings of the charger
subdevice of ACT8945A MFD.
Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Sebastian Reichel <sre@kernel.org>

Documentation/devicetree/bindings/power/act8945a-charger.txt

+Device-Tree bindings for charger of Active-semi ACT8945A Multi-Function Device
+
+Required properties:
+ - compatible: "active-semi,act8945a", please refer to ../mfd/act8945a.txt.
+ - active-semi,chglev-gpios: charge current level phandle with args
+   as described in ../gpio/gpio.txt.
+
+Optional properties:
+ - active-semi,check-battery-temperature: boolean to check the battery
+   temperature or not.
+ - active-semi,input-voltage-threshold-microvolt: unit: mV;
+   Specifies the charger's input over-voltage threshold value;
+   The value can be: 6600, 7000, 7500, 8000; default: 6600
+ - active-semi,precondition-timeout: unit: minutes;
+   Specifies the charger's PRECONDITION safety timer setting value;
+   The value can be: 40, 60, 80, 0; If 0, it means to disable this timer;
+   default: 40.
+ - active-semi,total-timeout: unit: hours;
+   Specifies the charger's total safety timer setting value;
+   The value can be: 3, 4, 5, 0; If 0, it means to disable this timer;
+   default: 3.
+
+Example:
+	pmic@5b {
+		compatible = "active-semi,act8945a";
+		reg = <0x5b>;
+		status = "okay";
+
+		pinctrl-names = "default";
+		pinctrl-0 = <&pinctrl_charger_chglev>;
+		active-semi,chglev-gpios = <&pioA 12 GPIO_ACTIVE_HIGH>;
+		active-semi,input-voltage-threshold-microvolt = <6600>;
+		active-semi,precondition-timeout = <40>;
+		active-semi,total-timeout = <3>;
+	};