Samsung Exynos4 GPIO Controller

Required properties:
- compatible: Compatible property value should be "samsung,exynos4-gpio>".

- reg: Physical base address of the controller and length of memory mapped
  region.

- #gpio-cells: Should be 4. The syntax of the gpio specifier used by client nodes
  should be the following with values derived from the SoC user manual.
     <[phandle of the gpio controller node]
      [pin number within the gpio controller]
      [mux function]
      [flags and pull up/down]
      [drive strength]>

  Values for gpio specifier:
  - Pin number: is a value between 0 to 7.
  - Flags and Pull Up/Down: 0 - Pull Up/Down Disabled.
                            1 - Pull Down Enabled.
                            3 - Pull Up Enabled.
          Bit 16 (0x00010000) - Input is active low.
  - Drive Strength: 0 - 1x,
                    1 - 3x,
                    2 - 2x,
                    3 - 4x

- gpio-controller: Specifies that the node is a gpio controller.
- #address-cells: should be 1.
- #size-cells: should be 1.

Example:

	gpa0: gpio-controller@11400000 {
		#address-cells = <1>;
		#size-cells = <1>;
		compatible = "samsung,exynos4-gpio";
		reg = <0x11400000 0x20>;
		#gpio-cells = <4>;
		gpio-controller;
	};
