[coreboot] Unable to build futility on 32-bit userspace

[Julius Werner]

FWIW, there should be no reason to build crossystem as part of
coreboot's compile-time utilities at all. crossystem is a helper meant
to run on the target device (the one that uses vboot-enabled
firmware), it doesn't make any sense to have it on the build machine.
We should fix the Makefiles so that they don't even pull this in, so
that coreboot can also be built on architectures that crossystem
doesn't support at all (e.g. SPARC or whatever). futility itself just
does some crypto stuff and should have no architecture-specific
components.