rockchip: RK3288 needs fdt and initrd below 256M now

I am not sure why this limit is changing. But my kernel
doesn't load when it's above 256. This was testing on the
rock2 board.

Signed-off-by: Sandy Patterson <apatterson@sightlogix.com>
Updated commit subject:
Signed-off-by: Simon Glass <sjg@chromium.org>