ECBM SystemProperty cleanup

- add a 'set' method in phone.java, and use it to set ECBM system property
  and mIsPhoneInEcmState variable
- use isInEcm() method in the phone.java to read mIsPhoneInEcmState

Test: manual
Bug: 30361624
Change-Id: Ib073915ea87ec2245ea568a6635f78be3141c226
6 files changed