linker_lists: Rework start/end macros to not rely on undefined behavior

Per the GCC bug listed below, the way we do linker lists is relying on
undefined behavior that seems to work in gcc, but doesn't always work in
clang. Andrew suggests rewriting our start/end macros in a different way
(as implemented here, from what he said in comment 1) to avoid these
problems.

Reported-by: AdityaK <appujee@google.com>
Suggested-by: Andrew Pinski <apinski@marvell.com>
Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108915


Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Andrew Pinski <apinski@marvell.com>