UBUNTU: SAUCE: (efi-lockdown) kexec_file: Disable at runtime if securelevel has been set

UBUNTU: SAUCE: (efi-lockdown) kexec_file: Disable at runtime if securelevel has been set

When KEXEC_VERIFY_SIG is not enabled, kernel should not loads image
through kexec_file systemcall if securelevel has been set.

This code was showed in Matthew's patch but not in git:
https://lkml.org/lkml/2015/3/13/778

Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: Lee, Chun-Yi <jlee@suse.com>
Signed-off-by: David Howells <dhowells@redhat.com>
(cherry picked from commit db0188224b6d4c9cd73205631fe8e30810fb19ab
 git://git.kernel.org/pub/scm/linux/kernel/git/jwboyer/fedora.git)
Signed-off-by: Seth Forshee <seth.forshee@canonical.com>