kbuild: add missing FORCE where $(call if_changed, ) is used

FORCE is needed for $(call if_changed,...) to be evaluated every time.
Otherwise, the command is not executed when the command line has
changed but any prerequisite has not been updated.

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