Add tee sink to SpdifStreamOut

Test: enable per https://source.android.com/docs/core/audio/debugging
      play ac3 track via SpdifStreamOut using
      AudioTrackSurroundTest#testPlayAC3Bytes
      dumpsys media.audio_flinger and see .raw iec61937 wrapped
      file in /data/misc/audioserver.
Change-Id: I65ccd9d8a5b92ef7ffc87e081095d8f7332d8acb