Input: elantech - export pressure and width when supported

Using the info of the Dell/Ubuntu driver, described in the protocol
document, report both width and pressure when pressing 1 and 3
fingers, for the versions of the touchpad which support it.

Signed-off-by: Éric Piel <eric.piel@tremplin-utc.net>
Reviewed-by: Henrik Rydberg <rydberg@euromail.se>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>