These drivers don't need to match any unit_directory type device.
They just need the id_table for module autoloading per module alias.

Not binding any of these drivers allows special-purpose drivers with
similar or same IDs to bind to devices.  This currently only benefits
out-of-tree drivers; on the other hand it is in no way detrimental to
in-tree drivers.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>