Input: elantech - add resolution query support for v4 hardware

It turns out that v4's firmware provides a command so we can query
the resolution. Let's use it.

Signed-off-by: JJ Ding <jj_ding@emc.com.tw>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>