improve cx_lowest logic

[Sean Bruno]

On Sun, 2012-07-08 at 03:22 -0700, Andriy Gapon wrote: 
> I would like to propose the following change for review and testing:
> http://people.freebsd.org/~avg/acpi_cpu_cx_lowest.diff

Very nice.  After a review I went ahead and applied it for testing.  All
seems to be well on battery and A/C on my T520 so I'm very happy to see
this go into the tree.

Let me know if you want me to do the man page update for acpi_cpu(4) 

Sean