Resync cmd, if_change, if_changed_dep, and if_changed_rule.

Clean up the users of if_changed_rule.

I deleted the modversions rule. It is dead code because barebox
does not define CONFIG_MODVERSIONS. It does not work without
scripts/genksyms/ anyway.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>