PL061 GPIO controller bindings

Required properties:
- compatible:
  - "arm,pl061", "arm,primecell".
- #gpio-cells : Should be two.
  - first cell is the gpio pin number
  - second cell is used to specify the gpio polarity:
      0 = active high
      1 = active low
- gpio-controller : Marks the device node as a GPIO controller.
- interrupt-controller : Marks the device node as an interrupt controller.
- #interrupt-cells : Should be two.
  - first cell is the hw irq number
  - second cell is used to specify the interrupt type:
      0 = default, unspecified type
      1 = rising edge triggered
      2 = falling edge triggered
      4 = high level triggered
      8 = low level triggered
- linux,gpio-base : Should be the global GPIO number.

Example:
	gpio0: gpio@fc806000 {
		compatible = "arm,pl061", "arm,primecell";
		reg = <0xfc806000 0x1000>;
		interrupts = <0 64 0x4>;
		gpio-controller;
		#gpio-cells = <2>;
		interrupt-controller;
		#interrupt-cells = <2>;
		linux,gpio-base = <0>;
	};
