USB polling (75% done)

[Hans Petter Selasky]

Hi,

I've added minimal polling support to the USB P4 repository now. Patch can be 
found here:

http://perforce.freebsd.org/chv.cgi?CH=166148

Dumping core to USB disk: Tested and works.

Using USB keyboard in KDB: Does not work because Giant is not locked when 
calling into the UKBD's get char routine. UKBD is Giant locked. Someone 
familiar with the keyboard system on FreeBSD please step forward and fix this  
so that UKBD gets independent of the Giant mutex.

--HPS