lmkd: allow lmkd to lock itself in memory

addresses the following denial:

  type=1400 audit(1.871:3): avc:  denied  { ipc_lock } for  pid=1406 comm="lmkd" capability=14  scontext=u:r:lmkd:s0 tcontext=u:r:lmkd:s0 tclass=capability

Bug: 16236289
Change-Id: Id9923c16c6db026dd5d28996126f503c5c1d7c87