* Atmel GPIO controller (PIO)

Required properties:
- compatible: "atmel,<chip>-gpio", where <chip> is at91rm9200 or at91sam9x5.
- reg: Should contain GPIO controller registers location and length
- interrupts: Should be the port interrupt shared by all the pins.
- #gpio-cells: Should be two.  The first cell is the pin number and
  the second cell is used to specify optional parameters (currently
  unused).
- gpio-controller: Marks the device node as a GPIO controller.

Example:
	pioA: gpio@fffff200 {
		compatible = "atmel,at91rm9200-gpio";
		reg = <0xfffff200 0x100>;
		interrupts = <2 4>;
		#gpio-cells = <2>;
		gpio-controller;
	};