[U-Boot] [PATCH 07/21] sandbox: Use 'extras' to specify 'head' files

[sjg at google.com]

At present sandbox has a start.o in the 'start' target but also includes
it in the normal target list. This is not how this is normally handled. It
is needed because sandbox does not include the u-boot-init variable in its
link rule.

Update the rule and move start.o from the normal target list to the
'extras' list.

Signed-off-by: Simon Glass <sjg at chromium.org>
---

 arch/sandbox/Makefile     | 4 ++--
 arch/sandbox/config.mk    | 3 ++-
 arch/sandbox/cpu/Makefile | 5 +++--
 3 files changed, 7 insertions(+), 5 deletions(-)

Applied to u-boot-dm/master, thanks!