Panic on shutdown, r243674M

[Ed Maste]

> Please try this patch:
> http://people.freebsd.org/~avg/acpi_cpu_notify.2.diff
>
> I should have committed this earlier, but the fact that we were not getting much
> problems when updating resources in place lead me to believe that we would not
> get more problems when first deleting and then re-creating resources.
>
> If the patch works OK, I'll commit it tomorrow.

It works fine for me (of course I can't say with certainty that I've
exercised the path that previously panicked).  Please go ahead and
commit.