audio: use FLAG_FAST for non-music stream on WFD

- Issue: WFD audio routes back to target speaker when
  starting a ringtone playback. Music and ringtone playback
  is mixed on target speaker. Expected behavior is music
  plays on WFD sink and ringtone plays on target speaker.

- Root cause:  primary output is created for music playback
  over WFD. The same primary output is reused for ringtone
  and output device is updated based on SONIFICATION strategy
  for both ringtone and music playback.
  The same issue is not seen on stock Android solution because
  two different HALs(remoted_submix for WFD audio and primary
  HAL for ringtone) are involved and primary output is not reused.

- Fix: update output flag to AUDIO_OUTPUT_FLAG_FAST when there
  is a non-music stream playback on WFD. So primary output is not
  reused for SONIFICATION strategy.
  Use AUDIO_EXTN_AFE_PROXY_ENABLED instead of WFD_CONCURRENCY to
  compile related code since WFD_CONCURRENCY is not enabled for
  all targets.

Change-Id: Id2f5965c8f5623646b2adb2aa892a9929f3bc5bb
CRs-Fixed: 745667