bloblist: Put the magic number first

It seems best to put the magic number right at the start of the bloblist
header, so it is easier to check. This is how devicetree works.

Make this change now, before other projects make use of bloblist. Other
changes may be needed / discussed, but that is TBD.

Add a checker function as well.

Signed-off-by: Simon Glass <sjg@chromium.org>
2 files changed