Create getSystemSelectionChannel API

Test: atest TelephonyManagerTest
Test: atest VtsHalRadioV1_6TargetTest
Bug: 152813408
Change-Id: I6f3f70b7ff1b876ec98086431ed5c557875fca85
Merged-In: I6f3f70b7ff1b876ec98086431ed5c557875fca85
4 files changed