Input: elantech - report position also with 3 fingers

The 6-byte protocol supports reporting the position when three fingers
are pressed, exactly like when one finger is pressed. Report this.

In addition, it is also distinguishes between 3 and 4 fingers pressed.

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