We have the capability to check regions written after U-Boot that
do not overlap. Since regions can also be written before U-Boot,
add such check for these too.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Andy Pont <andy.pont@sdcsystems.com>
Acked-by: Simon Glass <sjg@chromium.org>
Tested-by: Simon Glass <sjg@chromium.org>