init: Add support for native service registration with lmkd

init should be able to register native services with lmkd so that they
can be killed when needed. Only processes with oom_score_adjust not
equal to the default -1000 will be registered with lmkd because with the
score that low the process is unkillable anyway.
Inform lmkd when a registered process is killed so that the record can be
removed.
Change init.rc to start lmkd during init phase so that it is there to
register other services.
Replace hardcoded oom_score_adj values with appropriate definitions.

Bug: 129011369
Test: boot and verify native service registration
Change-Id: Ie5ed62203395120d86dc1c8250fae01aa0b3c511
Signed-off-by: Suren Baghdasaryan <surenb@google.com>