IPS driver: don't toggle CPU turbo on unsupported CPUs

If the CPU doesn't support turbo, don't try to enable/disable it.

http://bugzilla.kernel.org/show_bug.cgi?id=18742



Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Matthew Garrett <mjg@redhat.com>