This adds standard gadget_is_*() calls.  Gadget drivers using
those calls can get rid of some inlined #ifdefs, and will also
be able to do more "late binding" to their hardware.


Define gadget_is_*() calls, to help do late binding to USB controllers.

Current gadget drivers expect to know at compile time what hardware
they'll bind to.  That's not very friendly to a generic PDA distro,
which might prefer to defer such choices to run time.

These macros let drivers change that code from inlined #ifdefs (ugh) to
normal C statements (looks much nicer), so making those "what hardware"
policy choices at run time gets easier.