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

Test: Manual
Bug: 30361624
Change-Id: I23c3fa0c985efb28bf37f2d7ee1c85b732cc7b0d
5 files changed