mfd: fsl-imx25-tsadc: Register touchscreen ADC driver

This is the core driver for imx25 touchscreen/adc driver. The module
has one shared ADC and two different conversion queues which use the
ADC. The two queues are identical. Both can be used for general purpose
ADC but one is meant to be used for touchscreens.

This driver is the core which manages the central components and
registers of the TSC/ADC unit. It manages the IRQs and forwards them to
the correct components.

Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
Signed-off-by: Denis Carikli <denis@eukrea.com>
[ensure correct ADC clock depending on the IPG clock]
Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>