Input: touchscreen: Add imx25 TCQ driver

This is a driver for the imx25 ADC/TSC module. It controls the
touchscreen conversion queue and creates a touchscreen input device.
The driver currently only supports 4 wire touchscreens. The driver uses
a simple conversion queue of precharge, touch detection, X measurement,
Y measurement, precharge and another touch detection.

This driver uses the regmap from the parent to setup some touch specific
settings in the core driver and setup a idle configuration with touch
detection.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Denis Carikli <denis@eukrea.com>
[fix clock's period calculation]
[fix calculation of the 'settling' value]
Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>