Those won't have ABS_MT_* axes, so won't be reported has having
XITouchClassInfo. Fallback on these to checking whether abs x/y axes are
available. After the Wacom checks, any remaining device with absolute axes
should be touchscreens, and GDK_SOURCE_MOUSE does indeed just make sense on
devices with relative axes.
https://bugzilla.gnome.org/show_bug.cgi?id=757358