lowmemorykiller: Compact memory when killing processes

 * Memory compaction is never invoked on Android because we avoid swap
   and don't allocate huge pages. Fix it by invoking compaction from the LMK when
   a process is killed to reduce memory fragmentation.

Change-Id: I2bda790c2093e65fd6f43d52ea5149d6b57cb1e9
lowmemorykiller: Use asynchronous compaction

Change-Id: I6a65d06fc30b88fcedaaf1abf1855fdd19e3c912