Here's where all those preceding autoconfig patches start
to fit together:  one gadget driver gets rid of almost all
the controller-specific #ifdeffery.

Two of the other gadget drivers can do the same thing,
and just as easily:  file storage, and serial.  (I'll
hope their maintainers do those changes though.)

The "ether.c" gadget driver is a lot more complicated to
do this way since it has to cope with some differences
by switching to alternate protocols (CDC Ethernet vs
a subset) and soon be able to handle RNDIS.  So that'll
be a while yet.


Gadget Zero learns to autoconfigure.

    - Gets rid of remaining controller-specific #ifdeffery.  Now
      hardware choices can be made at run time too (not just
      compile time).

    - Simplifies its use of the "DEBUG" CPP symbol.

    - Force device to report itself consistently as self-powered.