Driver will log the last touch down event timestamp and expose it via sysfs. This feature utilized by sensors to mitigate false detection of back tap gestures. Change-Id: I2907acdf1a560a6ca923b9fc20243fef642d7b90 Signed-off-by: dengwei1 <dengwei1@motorola.com> Reviewed-on: https://gerrit.mot.com/2241177 SLTApproved: Slta Waiver SME-Granted: SME Approvals Granted Tested-by: Jira Key Reviewed-by: Wang Wang <wangwang1@lenovo.com> Submit-Approved: Jira Key