The next commit will add ldflags-y to scripts/Makefile.lib like Linux,
but barebox includes scripts/Makefile.lib from the top Makefile.

arch/mips/Makefile uses ldflags-y for a different meaning.

To avoid unpleasant side-effect, this commit rename it.

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