Input: wm97xx - add BTN_TOUCH event to wm97xx to use it with Android

Android expects BTN_TOUCH events when pen state changes. Add BTN_TOUCH
event reporting to allow use of wm97xx touchscreen controller wiht
Android devices.

Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>