Axis ETRAX FS General I/O controller bindings

Required properties:

- compatible: one of:
  - "axis,etraxfs-gio"
  - "axis,artpec3-gio"
- reg: Physical base address and length of the controller's registers.
- #gpio-cells: Should be 3
  - The first cell is the gpio offset number.
  - The second cell is reserved and is currently unused.
  - The third cell is the port number (hex).
- gpio-controller: Marks the device node as a GPIO controller.

Example:

	gio: gpio@b001a000 {
		compatible = "axis,etraxfs-gio";
		reg = <0xb001a000 0x1000>;
		gpio-controller;
		#gpio-cells = <3>;
	};