amd family 15h topology detection

Here is a patch that should prepare us for AMD Bulldozer CPUs:
http://people.freebsd.org/~avg/amd-f15h-topo.diff
The patch should not affect pre-10h systems at all, on 10h systems the new code
path should be taken, but the result should be the same as the legacy method.

P.S. I think that the legacy method will keep working with Bulldozer, but I am not
completely sure.  Anyway, I hope to find some time to improve our topology
detection code so that it doesn't assume uniformity and also takes into account
cache topology.  And then this change will be more useful.
-- 
Andriy Gapon