Add call event logging to telecom.

This code saves the last 5 calls and prints out all the call-related
events when doing a "dumpsys telecom".  This includes dumping all
information about the last 5 calls so that bug reports always contain
information about the calls.

Bug: 18923652

Change-Id: I4dbdea32ba4eea3b3a4158fbae99649dc045cd62