USB changes

[M. Warner Losh]

The time has come to reduce the #ifdefs that have grown to infest the
usb code.  The other BSDs have already done this to a greater or
lessor extent.  Many of the #ifdef sections have decayed and no longer
work on the target system.  There's been a number of cases where bugs
have resulted, and they generally make the code harder to read and
understand.

I'd like to remove many of the ifdefs, as well as expand many of the
portability hacks that are there.  I'll do my best to make sure that
each of the changes bring the files closer to style(9) as well as not
change the md5 of the .o file.

Comments?

Warner