Move lmkd into it's own domain.

lmkd low memory killer daemon

The kernel low memory killer logic has been moved to a new daemon
called lmkd.  ActivityManager communicates with this daemon over a
named socket.

This is just a placeholder policy, starting off in unconfined_domain.

Change-Id: Ia3f9a18432c2ae37d4f5526850e11432fd633e10