tools: moveconfig: add --force-sync option

tools: moveconfig: add --force-sync option

Now, this tools invokes "make savedefconfig" only when it needs to
do so, but there might be cases where a user wants the tool to do
savedefconfig forcibly, for example, some defconfigs were already
out of sync and the user wants to fix it as well.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>