mfd: Add documentation for ACT8945A DT bindings

The Active-semi ACT8945A PMIC is a Multi-Function Device, it has
two subdevices:
 - Regulator
 - Charger

This patch adds documentation for ACT8945A DT bindings.
Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/mfd/act8945a.txt

+Device-Tree bindings for Active-semi ACT8945A MFD driver
+
+Required properties:
+ - compatible: "active-semi,act8945a".
+ - reg: the I2C slave address for the ACT8945A chip
+
+The chip exposes two subdevices:
+ - a regulators: see ../regulator/act8945a-regulator.txt
+ - a charger: see ../power/act8945a-charger.txt
+
+Example:
+	pmic@5b {
+		compatible = "active-semi,act8945a";
+		reg = <0x5b>;
+		status = "okay";
+
+		pinctrl-names = "default";
+		pinctrl-0 = <&pinctrl_charger_chglev>;
+		active-semi,chglev-gpio = <&pioA 12 GPIO_ACTIVE_HIGH>;
+		active-semi,input-voltage-threshold-microvolt = <6600>;
+		active-semi,precondition-timeout = <40>;
+		active-semi,total-timeout = <3>;
+
+		active-semi,vsel-high;
+
+		regulators {
+			vdd_1v35_reg: REG_DCDC1 {
+				regulator-name = "VDD_1V35";
+				regulator-min-microvolt = <1350000>;
+				regulator-max-microvolt = <1350000>;
+				regulator-always-on;
+			};
+
+			vdd_1v2_reg: REG_DCDC2 {
+				regulator-name = "VDD_1V2";
+				regulator-min-microvolt = <1100000>;
+				regulator-max-microvolt = <1300000>;
+				regulator-always-on;
+			};
+
+			vdd_3v3_reg: REG_DCDC3 {
+				regulator-name = "VDD_3V3";
+				regulator-min-microvolt = <3300000>;
+				regulator-max-microvolt = <3300000>;
+				regulator-always-on;
+			};
+
+			vdd_fuse_reg: REG_LDO1 {
+				regulator-name = "VDD_FUSE";
+				regulator-min-microvolt = <2500000>;
+				regulator-max-microvolt = <2500000>;
+				regulator-always-on;
+			};
+
+			vdd_3v3_lp_reg: REG_LDO2 {
+				regulator-name = "VDD_3V3_LP";
+				regulator-min-microvolt = <3300000>;
+				regulator-max-microvolt = <3300000>;
+				regulator-always-on;
+			};
+
+			vdd_led_reg: REG_LDO3 {
+				regulator-name = "VDD_LED";
+				regulator-min-microvolt = <3300000>;
+				regulator-max-microvolt = <3300000>;
+				regulator-always-on;
+			};
+
+			vdd_sdhc_1v8_reg: REG_LDO4 {
+				regulator-name = "VDD_SDHC_1V8";
+				regulator-min-microvolt = <1800000>;
+				regulator-max-microvolt = <1800000>;
+				regulator-always-on;
+			};
+		};
+	};