Elantech I2C Touchpad

Required properties:
- compatible: must be "elan,ekth3000".
- reg: I2C address of the chip.
- interrupts: interrupt to which the chip is connected (see interrupt
  binding[0]).

Optional properties:
- wakeup-source: touchpad can be used as a wakeup source.
- pinctrl-names: should be "default" (see pinctrl binding [1]).
- pinctrl-0: a phandle pointing to the pin settings for the device (see
  pinctrl binding [1]).
- vcc-supply: a phandle for the regulator supplying 3.3V power.
- elan,trackpoint: touchpad can support a trackpoint (boolean)
- elan,clickpad: touchpad is a clickpad (the entire surface is a button)
- elan,middle-button: touchpad has a physical middle button
- elan,x_traces: number of antennas on the x axis
- elan,y_traces: number of antennas on the y axis
- some generic touchscreen properties [2]:
  * touchscreen-size-x
  * touchscreen-size-y
  * touchscreen-x-mm
  * touchscreen-y-mm


[0]: Documentation/devicetree/bindings/interrupt-controller/interrupts.txt
[1]: Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
[2]: Documentation/devicetree/bindings/input/touchscreen/touchscreen.txt

Example:
	&i2c1 {
		/* ... */

		touchpad@15 {
			compatible = "elan,ekth3000";
			reg = <0x15>;
			interrupt-parent = <&gpio4>;
			interrupts = <0x0 IRQ_TYPE_EDGE_FALLING>;
			wakeup-source;
		};

		/* ... */
	};
