mei: don't schedule suspend in pm idle

Calling pm_schedule_suspend from the runtime pm idle callback
may reschedule existing timer, thus in case of frequent runtime
rpm idle call the suspend maybe starved.
Instead we call pm_runtime_autosuspend which is checking if the
timer is already charged.

An example is monitoring device pci config space.
Pci config sysfs handlers calls pci_config_pm_runtime_put/get
helpers which in turns calls to device idle callback

Cc: stable@vger.kernel.org # 3.15+
Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>