Input: tsc2007 - add max_rt parameter to platform data

Finger touch events or very quick stylus events on low-quality panels
can cause the tsc2007 to read bogus values. Looking at oscilloscope
snapshots, this seems to be caused by the touch event disappearing
during the measurements. These bogus values result in misclicks, where
the X and Y values deviate from the real position.

Most of these misclicks can be filtered out by setting a low enough
threshold for the maximum resistance (which is loosely the inverse of
the pressure) allowed to consider a set of values valid. Since this
behaviour is largely dependent on the type and quality of the panel,
this commit introduces the max_rt parameter. The default value is kept
at MAX_12BIT.

Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>