Request for review/testing: G5 support

[Nathan Whitehorn]

I'd like to merge the G5 support currently in Perforce soon, to ensure 
some testing with it before the 8.0 code freeze. There are a few 
remaining bugs/issues listed below, but I think fixing them will be 
faster and easier once this is in the tree, and they are not serious 
issues in general. A diff against -CURRENT can be found at 
http://people.freebsd.org/~nwhitehorn/ppcg5.diff. If there is sufficient 
interest, I can make a CD image with the patch applied.

Notes:
- For SMU-based systems (later model Powermac G5s, and all G5 iMacs), 
there is currently no support for controlling the fans. Your machine 
will be loud.
- Adjusting the volume of the built-in audio on my G5 iMac does not work 
-- it is stuck at maximum
- PCI Express systems likely do not work.
- SMP is currently tested only on an emulator, where it works fine -- 
I'd appreciate any test reports
- Serial consoles seem to be broken at the moment
- If you set CPUTYPE=970 in make.conf, be *absolutely sure* to add 
-mno-powerpc64 to CFLAGS, or you will get strange runtime errors.

Everything else (built-in devices, X, etc.) should work. Please let me 
know how it goes if you try the patch!
-Nathan