trace: allow memkill tracing to be selectively enabled

Change-Id: I8a50d6b121192b0dc94e2a9a0e05246a47045e81
Signed-off-by: Jeffrey Carlyle <jeff.carlyle@motorola.com>
Reviewed-on: http://gerrit.pcs.mot.com/482673
Reviewed-on: http://gerrit.pcs.mot.com/513906
Tested-by: Jira Key <jirakey@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>
Submit-Approved: Jira Key <jirakey@motorola.com>
(cherry picked from commit fd9bd32cd8f005b0d2f6438935fdd0bc9654c938)