The RK3399 supports close the center logic enter power mode,
so we can close PD_CENTER to save more power during suspend.
Therefore, we need to support save/restore the DDR PHY and
controller registers during suspend/resume.

Also, need CL (http://crosreview.com/397399) to check disabling
center logic.

Change-Id: I288defd8e9caa3846d9fa663a33e4d51df1aaa5d
Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>
Signed-off-by: Derek Basehore <dbasehore@chromium.org>
Signed-off-by: Caesar Wang <wxt@rock-chips.com>