Samsung tm2-touchkey

Required properties:
- compatible:
    * "cypress,tm2-touchkey" - for the touchkey found on the tm2 board
    * "cypress,midas-touchkey" - for the touchkey found on midas boards
    * "cypress,aries-touchkey" - for the touchkey found on aries boards
- reg: I2C address of the chip.
- interrupts: interrupt to which the chip is connected (see interrupt
	binding[0]).
- vcc-supply : internal regulator output. 1.8V
- vdd-supply : power supply for IC 3.3V

Optional properties:
- linux,keycodes: array of keycodes (max 4), default KEY_PHONE and KEY_BACK

[0]: Documentation/devicetree/bindings/interrupt-controller/interrupts.txt

Example:
	&i2c0 {
		/* ... */

		touchkey@20 {
			compatible = "cypress,tm2-touchkey";
			reg = <0x20>;
			interrupt-parent = <&gpa3>;
			interrupts = <2 IRQ_TYPE_EDGE_FALLING>;
			vcc-supply=<&ldo32_reg>;
			vdd-supply=<&ldo33_reg>;
			linux,keycodes = <KEY_PHONE KEY_BACK>;
		};
	};