evdev: enable button scrolling by default on mice without wheels

evdev: enable button scrolling by default on mice without wheels

If we have a middle button but no wheels, enable on-button scrolling for the
middle button by default. This applies e.g. to the Logitech trackball added as
new test device here.

This makes the separate check for POINTINGSTICK obsolete but I'd rather leave
this in to be more explicit about it.

https://bugs.freedesktop.org/show_bug.cgi?id=90208

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