The code to initiate and exit the powerdown sequence is the same in
pm.c and cpuidle.c.

Let's split the common part in the pm.c and reuse it from the cpu_pm notifier.

That is one more step forward to make the cpuidle driver arch indenpendant.
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>