ideapad_laptop: introduce #ifdef CONFIG_PM_SLEEP for PM specific code

ideapad_acpi_resume() and ideapad_pm is meaningful
only if CONFIG_PM_SLEEP is set.
Thus introduce #ifdef for this piece of code.

Signed-off-by: Zhang Rui <rui.zhang@intel.com>
CC: Matthew Garrett <matthew.garrett@nebula.com>
CC: Ike Panhc <ike.pan@canonical.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>