uboot-imx

rockchip: rk3328: correct mem_region

According to rk3328 TRM:
0~0xff000000 is ddr space;
0xff000000~0xffffffff is device space.

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>