rockchip: clk: rk3188: change APLL to safe 600MHz

rockchip: clk: rk3188: change APLL to safe 600MHz

The commit 52213f060fb6 ("rockchip: rk3188: init CPU freq in clock
driver") changed ARM clock from 600MHz to 1600MHz. It made boot
unstable due to the fact that PMIC at the start generates insufficient
voltage for operation. See also: commit 51536d29c510 ("rockchip:
rk3188: Setup the armclk in spl").

Fixes commit 52213f060fb6 ("rockchip: rk3188: init CPU freq in clock
driver").

Signed-off-by: Alexander Kochetkov <al.kochet@gmail.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>