* Phytium GPIO controller

Required properties:
- compatible : Should contain "phytium,gpio"
- reg : Address and length of the register set for the device.
- interrupts: Interrupt mapping for GPIO IRQ.
- gpio-controller : Marks the device node as a gpio controller.
- #gpio-cells : Should be 2. The first cell is the pin number and
  the second cell is used to specify the gpio polarity:
      0 = active high
      1 = active low
- #address-cells : should be 1 (for addressing port subnodes).
- #size-cells : should be 0 (port subnodes).

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

Required properties:
- compatible : "phytium,gpio-port"
- reg : The integer port index of the port, a single cell.

Optional properties:
- nr-gpios : The number of pins in the port, a single cell.

Example:

gpio: gpio@28004000 {
	compatible = "phytium,gpio";
	reg = <0x0 0x28004000 0x0 0x1000>;
	interrupts = <GIC_SPI 10 IRQ_TYPE_LEVEL_HIGH>;
	gpio-controller;
	#gpio-cells = <2>;
	#address-cells = <1>;
	#size-cells = <0>;

	porta {
		compatible = "phytium,gpio-port";
		reg = <0>;
		nr-gpios = <8>;
	};

	portb {
		compatible = "phytium,gpio-port";
		reg = <1>;
		nr-gpios = <8>;
	};
};
