Allow secondary ids missing for DAB selector

Sometimes DAB program selector used in tuning does not have secondary
identifiers such as ensemble and frequency, and HAL will automatically
selector a DAB station with specified ensemble and frequency. Thus,
secondary ids in DAB program selector are not mandatory in HAL. Also
updated broadcast radio AIDL HAL documentation.

Bug: 273804622
Test: atest VtsHalBroadcastradioAidlTargetTest
Change-Id: If05b7eeb79e299667c3a64bf8b931bb6396f9045