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

Describe the bindings for EETI touchscreen controllers.
Signed-off-by: Daniel Mack <daniel@zonque.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/touchscreen/eeti.txt

+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>;
+	};
+};