Input: add binding documentation for imx25 touchscreen controller

Freescale mx25 TS conversion queue module

mx25 touchscreen conversion queue module which controls the ADC unit of the

mx25 for attached touchscreens.

Required properties:

 - compatible: Should be "fsl,imx25-tcq".

 - reg: Memory range of the device.

 - interrupts: Should be the interrupt number associated with this module within

   the tscadc unit (<0>).

 - interrupt-parent: Should be a phandle to the tscadc unit.

 - fsl,wires: Should be '<4>' or '<5>'

Optional properties:

 - fsl,pen-debounce-ns: Pen debounce time in nanoseconds.

 - fsl,pen-threshold: Pen-down threshold for the touchscreen. This is a value

   between 1 and 4096. It is the ratio between the internal reference voltage

   and the measured voltage after the plate was precharged. Resistence between

   plates and therefore the voltage decreases with pressure so that a smaller

   value is equivalent to a higher pressure.

 - fsl,settling-time-ns: Settling time in nanoseconds. The settling time is before

   the actual touch detection to wait for an even charge distribution in the

   plate.

This device includes two conversion queues which can be added as subnodes.

The first queue is for the touchscreen, the second for general purpose ADC.

Example:

	tsc: tcq@50030400 {

		compatible = "fsl,imx25-tcq";

		reg = <0x50030400 0x60>;

		interrupt-parent = <&tscadc>;

		interrupts = <0>;

		fsl,wires = <4>;

	};