Input: elantech - provide a workaround for jumpy cursor on firmware 2.34

It seems that Elantech touchpad firmware version 2.34 on the Hercules eCAFÉ
suffers from a problem where bogus coordinates get reported at the beginning
of a touch action. This causes the mouse cursor or the scrolled page to
jump.

Included patch provides a workaround that discards mouse packets that are
likely to contain bogus coordinates. The workaround is activated when we
detect touchpad with fimware version 2.34.

Signed-off-by: Arjan Opmeer <arjan@opmeer.net>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>