dt-bindings: mfd: Add DT bindings for max77650

Add a DT binding document for max77650 ultra-low power PMIC. This
describes the core mfd device and the GPIO module.

Signed-off-by: Bartosz Golaszewski <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Acked-by: Pavel Machek <[e-mail]>
Signed-off-by: Lee Jones <[e-mail]>

Documentation/devicetree/bindings/mfd/max77650.txt

···
+MAX77650 ultra low-power PMIC from Maxim Integrated.
+
+Required properties:
+-------------------
+- compatible:		Must be "maxim,max77650"
+- reg:			I2C device address.
+- interrupts:		The interrupt on the parent the controller is
+			connected to.
+- interrupt-controller: Marks the device node as an interrupt controller.
+- #interrupt-cells:	Must be <2>.
+
+- gpio-controller:	Marks the device node as a gpio controller.
+- #gpio-cells:		Must be <2>. The first cell is the pin number and
+			the second cell is used to specify the gpio active
+			state.
+
+Optional properties:
+--------------------
+gpio-line-names:	Single string containing the name of the GPIO line.
+
+The GPIO-controller module is represented as part of the top-level PMIC
+node. The device exposes a single GPIO line.
+
+For device-tree bindings of other sub-modules (regulator, power supply,
+LEDs and onkey) refer to the binding documents under the respective
+sub-system directories.
+
+For more details on GPIO bindings, please refer to the generic GPIO DT
+binding document <devicetree/bindings/gpio/gpio.txt>.
+
+Example:
+--------
+
+	pmic@48 {
+		compatible = "maxim,max77650";
+		reg = <0x48>;
+
+		interrupt-controller;
+		interrupt-parent = <&gpio2>;
+		#interrupt-cells = <2>;
+		interrupts = <3 IRQ_TYPE_LEVEL_LOW>;
+
+		gpio-controller;
+		#gpio-cells = <2>;
+		gpio-line-names = "max77650-charger";
+	};