Input: elantech - improve clickpad detection

The current assumption in the elantech driver that hw version 3 touchpads
are never clickpads and hw version 4 touchpads are always clickpads is
wrong.

There are several bug reports for this, ie:
https://bugzilla.redhat.com/show_bug.cgi?id=1030802
http://superuser.com/questions/619582/right-elantech-touchpad-button-not-working-in-linux



I've spend a couple of hours wading through various bugzillas, launchpads
and forum posts to create a list of fw-versions and capabilities for
different laptop models to find a good method to differentiate between
clickpads and versions with separate hardware buttons.

Which shows that a device being a clickpad is reliable indicated by bit 12
being set in the fw_version. I've included the gathered list inside the
driver, so that we've this info at hand if we need to revisit this later.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>