The ATAG_CORE is allowed to be empty. Although this is handled
by parse_tag_core(), __vet_atags during startup rejects this tag
unless it contains data. Allow the initial tag to be either the
full size, or empty.
Signed-off-by: David Brown <davidb@quicinc.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>