[CFT]hwpmc update for sandybridge-e

[Sean Bruno]

So, I did the bear minimum and kind of hacked things together without
understanding precisely what I was doing, and I was able to massage the
sandybridge-e CPUs into giving me some basic functions.

Comments or concerns before I commit this?

http://people.freebsd.org/~sbruno/pmc_sandybridge.txt

Sean

p.s.  I'm trying to hunt down some IvyBridge boxes to finish this off.