Preliminary ADB support

[Nathan Whitehorn]

I've spent the last couple of days trying to get ADB support going on my 
Powermac G3. Now that I've met with some success (I'm typing this on an 
ADB keyboard), I felt I should share the results.

The current code (supports only CUDA controllers, not PMU-attached buses, 
and the mouse support isn't complete) can be found here:

http://hep.uchicago.edu/~nathanw/freebsd_adb.tgz

I'm going to finish hooking up the mouse code in the next couple days, and 
will then investigate adding a PMU driver. I don't generally have access 
to machines with this part, though.

Most of the copyrights are also worng in the above. The CUDA driver is 
mostly copied from NetBSD.
-Nathan