Enable passthrough mode by default for audio, soundtrigger, and radio

Remove ENABLE_TREBLE flag usage for legacy hal fallback.
Introduce new build flag USE_LEGACY_LOCAL_AUDIO_HAL for fallback.

Bug: 32978887
Test: checked "OK Google" (from standby), Hangouts, YouTube,
      Play Music, fake radio hal + test app
KI: issues when using equializer and virtualuzer in Play Music

Change-Id: I1c279e622c885f799481f1287e0660ca576fcea0