* Synopsys DesignWare APB GPIO controller

Required properties:
- compatible : Should contain "snps,dw-apb-gpio"
- reg : Address and length of the register set for the device.
- #address-cells : should be 1 (for addressing port subnodes).
- #size-cells : should be 0 (port subnodes).

The GPIO controller has a configurable number of ports, each of which are
represented as child nodes with the following properties:

Required properties:
- compatible : "snps,dw-apb-gpio-port"
- gpio-controller : Marks the device node as a gpio controller.
- #gpio-cells : Should be two.  The first cell is the pin number and
  the second cell is used to specify the gpio polarity:
      0 = active high
      1 = active low
- reg : The integer port index of the port, a single cell.

Optional properties:
- interrupt-controller : The first port may be configured to be an interrupt
controller.
- #interrupt-cells : Specifies the number of cells needed to encode an
  interrupt.  Shall be set to 2.  The first cell defines the interrupt number,
  the second encodes the triger flags encoded as described in
  Documentation/devicetree/bindings/interrupts.txt
- interrupt-parent : The parent interrupt controller.
- interrupts : The interrupt to the parent controller raised when GPIOs
  generate the interrupts.
- snps,nr-gpios : The number of pins in the port, a single cell.

Example:

gpio: gpio@20000 {
	compatible = "snps,dw-apb-gpio";
	reg = <0x20000 0x1000>;
	#address-cells = <1>;
	#size-cells = <0>;

	porta: gpio-controller@0 {
		compatible = "snps,dw-apb-gpio-port";
		gpio-controller;
		#gpio-cells = <2>;
		snps,nr-gpios = <8>;
		reg = <0>;
		interrupt-controller;
		#interrupt-cells = <2>;
		interrupt-parent = <&vic1>;
		interrupts = <0>;
	};

	portb: gpio-controller@1 {
		compatible = "snps,dw-apb-gpio-port";
		gpio-controller;
		#gpio-cells = <2>;
		snps,nr-gpios = <8>;
		reg = <1>;
	};
};