Mark all files used in a standard build of bin-x86_64-efi/snponly.efi
as permitted for UEFI Secure Boot.  These files represent the core
functionality of iPXE that is guaranteed to have been included in
every binary that was previously subject to a security review and
signed by Microsoft.  It is therefore legitimate to assume that at
least these files have already been reviewed to the required standard
multiple times.

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