Input: tsc2007 - debounce pressure measurement

When the controller signals a pen-down event via the platform-specific
GPIO, while the sample values indicate an invalid measurement, the
measurement needs to be repeated.

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