dt-bindings: input: touchscreen: add bindings for eeti touchscreen controller

Bindings for EETI touchscreen controller

Required properties:

- compatible:	should be "eeti,exc3000-i2c"

- reg:		I2C address of the chip. Should be set to <0xa>

- interrupts:	interrupt to which the chip is connected

Optional properties:

- attn-gpios:	A handle to a GPIO to check whether interrupt is still

		latched. This is necessary for platforms that lack

		support for level-triggered IRQs.

The following optional properties described in touchscreen.txt are

also supported:

- touchscreen-inverted-x

- touchscreen-inverted-y

- touchscreen-swapped-x-y

Example:

i2c-master {

	touchscreen@a {

		compatible = "eeti,exc3000-i2c";

		reg = <0xa>;

		interrupt-parent = <&gpio>;

		interrupts = <123 IRQ_TYPE_EDGE_RISING>;

		attn-gpios = <&gpio 123 GPIO_ACTIVE_HIGH>;

	};

};