Make CellBroadcast APIs public

Also includes permission checks for enable/disable range, which
Require RECEIVE_EMERGENCY_BROADCAST.

Bug: 135956699
Test: Manually verify that CellBroadcastRecevier is able to call, verify
with CTS that without permissions a SecurityException is thrown
Change-Id: I3ee6c81b353f707caff13f5906b8dc6a66487267
3 files changed