Input: elantech - discard the first 2 positions on some firmwares

According to the Dell/Ubuntu driver, what was previously observed as
"jumpy cursor" corresponds to the hardware sending incorrect data for
the first two reports of a one touch finger. So let's use the same
workaround as in the other driver. Also, detect another firmware
version with the same behaviour, as in the other driver.

Signed-off-by: Éric Piel <eric.piel@tremplin-utc.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>