ARM: EXYNOS: Call regulator core suspend prepare and finish functions

The regulator framework has a set of helpers functions to be used when
the system is entering and leaving from suspend but these are not called
on Exynos platforms. This means that the .set_suspend_* function handlers
defined by regulator drivers are not called when the system is suspended.

Suggested-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>