This was originally intended as a fixed xorg.conf option only (and still
largely is seen as such). Secondary software button are required only on a specific series
of touchpads and should be pre-configured by the system and/or the
distribution. As such, the property will not be initialized if it is not set
in the xorg.conf and will thus not respond to runtime changes.

Exposing the property in this way gives clients a chance of detecting if a top
software button area is present and thus adjust their behaviour accordingly.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>