Input: wm97xx - add Palm support to Mainstone accelerated touch

This patch refactors the Mainstone accelerated touch code a little and
adds support for interrupt driven touchscreen on Palm LifeDrive, TX and
Tungsten T5.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>