Starting with v3 hardware, the firmware supports this shorter
elantech_send_cmd. Teach the driver to use it.
Signed-off-by: NJJ Ding <jj_ding@emc.com.tw>
Reviewed-by: NDaniel Kurtz <djkurtz@chromium.org>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>