IPS driver: apply BIOS provided CPU limit if different from default

The BIOS may hand us a lower CPU power limit than the default for a
given SKU.  We should use it in case the platform isn't designed to
dissapate the full TDP of a given part.

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