vt(4) support on SPARC

[Nathan Whitehorn]

I'm hoping to collect test results for the patch at 
http://people.freebsd.org/~nwhitehorn/vt-sparc64.diff

It does the following things:
1. Adds vt to SPARC64 GENERIC as a run-time selectable feature. syscons 
is still the default, but you can try vt by setting kern.vty=vt at the 
boot loader.
2. Fix some bitrot in the sparc64 support in ofwfb, so that it compiles 
again on SPARC.
3. Removes some of the PCI-focused aspects of ofwfb and adds some other 
improvements to it (not all of them SPARC-related).

This should work at least on all systems currently using machfb(4) and 
provides a working graphics console on my Ultra 5. It likely doesn't 
work on systems using creatorfb(4) -- I believe that will require a 
different driver -- though I would very much appreciate test results on 
such systems. It may also work on some systems that currently have no 
working graphics console at all.

So, if you have a SPARC system with video hardware, I would really 
appreciate it if you could give this a try. If you don't set kern.vty at 
the loader prompt, it should not change anything.

If you try it on a non-Mach64 system and it provides a working console, 
please let me know. If you try it and it does not work (no matter what 
kind of graphics hardware), please also let me know and tell me what 
kind of graphics card you have and send the output of "ofwdump -p 
screen". Any other comments or test results would also be appreciated.
-Nathan