Input: wacom_w8001 - support (and ignore) touch tablets

Tablets that support touch input may report different sized packages,
depending on the touch sensor in the tablet. For now, discard the
packages until we report them as touch input proper.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>