Input: elantech - add support for newer (August 2013) devices

Added detection for newer Elantech touchpads, so that kernel doesn't
fall-back to default PS/2 driver. Supports touchpads released after
~August 2013.  Fixes bug:
https://lists.launchpad.net/kernel-packages/msg18481.html



Tested on an Acer Aspire S7-392-6302.

Signed-off by: Matt Walker <matt.g.d.walker@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>