lmkd: Add ability to trace lmkd kills

For tracing lmkd kills inside kernel it is useful to have traces
indicating when and which process lmkd is killing. By default the
tracing is disabled.

Bug: 63631020
Test: alloc-stress

Change-Id: I3ceb2bde0c292eec55855cb4535927f3b4c5d08b
Signed-off-by: Suren Baghdasaryan <surenb@google.com>