ECBM SystemProperty cleanup

- Add getEmergencyCallbackMode() method to get the boolean
value for ECBM callback mode from the phone, in the
PhoneInterfaceManager.java

- Replace the 'get' of PROPERTY_INECM_MODE system property
in the packages/services/Telephony

Change-Id: Ide35e28b3339f58523bfe92be3c2fdfce111d45e
Test: Manual
Bug: 30361624
5 files changed