rockchip: rk3288: correct sdram setting

The DMC driver in v3.14 kernel[0] get the ddr setting from PMU_SYS_REG2,
and it expects uboot to store the value using a same protocol. But now
the ddr setting value is different with DMC, so if you enable the DMC,
system would crash in kernel. Correct the sdram setting here, according
to the requirements of kernel.

[0]
https://chromium.googlesource.com/chromiumos/third_party/kernel/+/


chromeos-3.14/drivers/clk/rockchip/clk-rk3288-dmc.c

Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>