BluetoothAudioHAL: Have full initialization for audio hardware objects

Audio frameworks usually check whether a module has specific features by
particular function pointers, and must be null if unsupported. If a
module is not fully initialized, some pointers would be undefined, but
causes abnormal crashes when accessed by audio frameworks.  

Bug: 152379666
Test: manually
Change-Id: Id6a79b651f2acbd35bd509ba36a80adea5c13e05