Show time stamp of missed call notification created by Telecom

If a default dialer does not implement
"android.telecom.action.SHOW_MISSED_CALLS_NOTIFICATION" receiver,
a missed call notification created by Telecom is shown. But the
time stamp information in the notification is missing. So, added
time stamp of missed call notification.

Test: manual - Checked the time stamp on Telecom missed call
notification
Bug: 62644406

Change-Id: Ica1ff913106b35f0690a566df330b4ea64c2fe5d