evdev: hook up a generic enable/disable interface for devices

evdev: hook up a generic enable/disable interface for devices

The evdev fallback dispatch supports enabling and disabling devices. That's
fairly easy to support since we don't (yet) have extra event generation within
the fallback backend. Thus, we can simply close the fd and re-open it again
later.

Touchpads are currently excluded here, they generate extra events on tapping,
scrolling, and software buttons and need a more complex implementation.

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