build(makefile): add helper to detect linker options

This is a small helper to check for possible linker options. If the
linker supports the requested option it is returned and if not nothing
will be returned, e.g.:

  TF_LDFLAGS += $(call ld_option, --no-warn-rwx-segments)

can be called unconditional.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Change-Id: I236800852ece49948ff53a0b91fddba53c8f0f95
1 file changed