Multi machine barebox builds have to pass information on which
board we are running on via boarddata. Usually this will be a
pointer to a device tree. Some boards might not have a device
tree available though because they are either not ported over
to device tree yet, or are running in some limited first state
environment which does not offer enough space for a device
tree. For these cases this patch adds a mechanism to embed a
machine number into a struct type along with a magic number.
This makes it possible to check for a specific machine
later during regular runtime.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>