Add missing FILE_LICENCE declarations to x86_64 headers based on the
corresponding i386 headers (from which the x86_64 headers were
originally derived).

Signed-off-by: Michael Brown <mcb30@ipxe.org>

Currently the only supported platform for x86_64 is EFI.

Building an EFI64 gPXE requires a version of gcc that supports
__attribute__((ms_abi)).  This currently means a development build of
gcc; the feature should be present when gcc 4.4 is released.

In the meantime; you can grab a suitable gcc tree from

  git://git.etherboot.org/scm/people/mcb30/gcc/.git