Multiboot is an x86 only thing. Drop support on ARM.
Change-Id: I13fafa464a794206d5450b4a1f23a187967a8338
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/2392
Tested-by: build bot (Jenkins)
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>