mfd: Add DT binding documentation for imx25 ADC/TSC

Freescale MX25 ADC/TSC MultiFunction Device (MFD)

This device combines two general purpose conversion queues one used for general

ADC and the other used for touchscreens.

Required properties:

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

 - reg:				Start address and size of the memory area of

 					the device

 - interrupts:			Interrupt for this device

					(See: ../interrupt-controller/interrupts.txt)

 - clocks:			An 'ipg' clock (See: ../clock/clock-bindings.txt)

 - interrupt-controller:	This device is an interrupt controller. It

   					controls the interrupts of both

					conversion queues.

 - #interrupt-cells:		Should be '<1>'.

 - #address-cells:		Should be '<1>'.

 - #size-cells:			Should be '<1>'.

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:

	tscadc: tscadc@50030000 {

		compatible = "fsl,imx25-tsadc";

		reg = <0x50030000 0xc>;

		interrupts = <46>;

		clocks = <&clks 119>;

		clock-names = "ipg";

		interrupt-controller;

		#interrupt-cells = <1>;

		#address-cells = <1>;

		#size-cells = <1>;

		ranges;

		tsc: tcq@50030400 {

			compatible = "fsl,imx25-tcq";

			reg = <0x50030400 0x60>;

			...

		};

		adc: gcq@50030800 {

			compatible = "fsl,imx25-gcq";

			reg = <0x50030800 0x60>;

			...

		};

	};