lsm: rework the LSM enable/disable setter/getter functions

lsm: rework the LSM enable/disable setter/getter functions

In addition to style changes, rename set_enabled() to lsm_enabled_set()
and is_enabled() to lsm_is_enabled() to better fit within the LSM
initialization code.

Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
Reviewed-by: John Johansen <john.johhansen@canonical.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>