FreeBSD loader always passes "elf kernel". We currently pass "elf64 kernel"
when loading 64-bit kernel. The -CURRENT, HEAD, kernel accepts only
"elf kernel". Older kernel accepts either.
Tested with FreeBSD and DragonFlyBSD.
Reference: https://cgit.freebsd.org/src/commit/?id=b72ae900d4348118829fe04abdc11b620930c30f
Signed-off-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>