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: NDaniel Lezcano <daniel.lezcano@linaro.org>
Reviewed-by: NViresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: NBartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Reviewed-by: NTomasz Figa <t.figa@samsung.com>
Signed-off-by: NKukjin Kim <kgene.kim@samsung.com>