Input: elantech - v4 is a clickpad, with only one button

Add pointer and buttonpad properties for v4 hardware.

Also, Jachiet reported that on Asus UX31, right button has no effect.
It turns out v4 has only one button, the right-button effect is
implemented with software when Windows driver is installed, or in
firmware when touchpad is in relative mode. So remove BTN_RIGHT
while at it.

Reported-by: Jachiet Louis <louis@jachiet.com>
Signed-off-by: JJ Ding <jj_ding@emc.com.tw>
Reviewed-by: Chase Douglas <chase.douglas@canonical.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>