trace: memkill: trace LMK and OOM kills

How to enable tracer:

  # mount -t debugfs nodev /sys/kernel/debug
  # echo 1 > /sys/kernel/debug/tracing/tracing_on
  # echo 1 > /sys/kernel/debug/tracing/events/memkill/enable
  # cat /sys/kernel/debug/tracing/trace

Event format:

  oom_kill: <pid> <comm> <total_vm> <anon_rss> <file_rss> <oom_score_adj> <order> <points> <cached> <freeswap>
  oom_kill_shared: <pid> <comm>
  lmk_kill: <pid> <comm> <selected_oom_adj> <selected_tasksize> <min_adj> <cached> <freeswap>

Change-Id: Ic45e181c62aead9b19d2a40363217f9220896096
Signed-off-by: Jeffrey Carlyle <jeff.carlyle@motorola.com>
Reviewed-on: http://gerrit.pcs.mot.com/480746
Reviewed-on: http://gerrit.pcs.mot.com/513174
Tested-by: Jira Key <jirakey@motorola.com>
Reviewed-by: Jason Hrycay <jason.hrycay@motorola.com>
Reviewed-by: Klocwork kwcheck <klocwork-kwcheck@sourceforge.mot.com>
Reviewed-by: Thirumarai Selvi S <a16462@motorola.com>
Reviewed-by: Check Patch <CHEKPACH@motorola.com>
Reviewed-by: Christopher Fries <qcf001@motorola.com>
Submit-Approved: Jira Key <jirakey@motorola.com>
(cherry picked from commit ef733ddfbb73cd33daf36720fa474ce4c8acb1f7)