ANDROID: lowmemorykiller: trace kill events.

Allows for capturing lmk kill events and
their rationale.

Change-Id: I74404e1a7e390a8a34fdd8020c25e5554d9e053d
Signed-off-by: Martijn Coenen <maco@google.com>
Git-Commit: cbd47bd62399911c7e95ce82314c660e44a05e61
Git-Repo: https://android.googlesource.com/kernel/common


Signed-off-by: Patrick Daly <pdaly@codeaurora.org>