LSM: Ignore "security=" when "lsm=" is specified

To avoid potential confusion, explicitly ignore "security=" when "lsm=" is
used on the command line, and report that it is happening.

Suggested-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Casey Schaufler <casey@schaufler-ca.com>
Acked-by: John Johansen <john.johansen@canonical.com>
Signed-off-by: James Morris <james.morris@microsoft.com>