Input: elantech - add v3 hardware support

v3 hardware's packet format is almost identical to v2 (one/three finger touch),
except when sensing two finger touch, the hardware sends 12 bytes of data.

Signed-off-by: JJ Ding <jj_ding@emc.com.tw>
Acked-by: Daniel Kurtz <djkurtz@chromium.org>
Acked-by: Éric Piel <eric.piel@tremplin-utc.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>