libfdt: migrate fdt_wip.c to a wrapper of scripts/dtc/libfdt/fdt_wip.c

Now, lib/libfdt/fdt_wip.c is the same as scripts/dtc/libfdt/fdt_wip.c

Change the former to a wrapper of the latter.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Simon Glass <sjg@chromium.org>