cbfs: Move static variables into a struct

At present there are a number of static variables in BSS. This cannot work
with SPL, at least until BSS is available in board_init_r().

Move the variables into a struct, so it is possible to malloc() it and use
it before BSS is available.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>