PM / mfd: intel-lpss: Use DPM_FLAG_SMART_SUSPEND

Make the intel-lpss driver set DPM_FLAG_SMART_SUSPEND for its
devices which will allow them to stay in runtime suspend during
system suspend unless they need to be reconfigured for some reason.

Also make it avoid resuming its child devices if they have
DPM_FLAG_SMART_SUSPEND set to allow them to remain in runtime
suspend during system suspend.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-for-MFD-by: Lee Jones <lee.jones@linaro.org>
Tested-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>