UPSTREAM: clk: rockchip: switch PLLs to slow mode before reboot for rk3288

UPSTREAM: clk: rockchip: switch PLLs to slow mode before reboot for rk3288

We've been seeing some crashes at reboot test on rk3288-based systems,
which boards have not reset pin connected to NPOR, they reboot by
setting 0xfdb9 to RK3288_GLB_SRST_FST register. If the APLL works in
a high frequency mode, some IPs might hang during soft reset.
It appears that we can fix the problem by switching to slow mode before
reboot, just like what we did before suspend.

Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
(cherry picked from commit 1d33929e2a2b69ae6d40e09ccfc8c7d705a543ba)

Change-Id: Ic01f80e6f33ae84cc87e954aae35f26b6f1a5434
Signed-off-by: Xing Zheng <zhengxing@rock-chips.com>