This moves the multiboot header into its own include file, simplifying
head.S and making it easier to include/exclude the multiboot header
based on config options.
BUG=b:242829490
TEST=Able to build and boot google/rex.
Change-Id: I59a22dfe36044b4dd64a5b028a134be7a7d02a48
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82533
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
