intel_idle: disable NHM/WSM HW C-state auto-demotion

commit 14796fca2bd22acc73dd0887248d003b0f441d08 upstream.

Hardware C-state auto-demotion is a mechanism where the HW overrides
the OS C-state request, instead demoting to a shallower state,
which is less expensive, but saves less power.

Modern Linux should generally get exactly the states it requests.
In particular, when a CPU is taken off-line, it must not be demoted, else
it can prevent the entire package from reaching deep C-states.

https://bugzilla.kernel.org/show_bug.cgi?id=25252

Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>