IMS-VT: Correctly route audio on headset plugged out

- When a wired headset has been plugged in, keep track of any
  upgrade/downgrade requests and update the fallback audio
  hint to either EARPIECE or SPEAKER

- Once headset is plugged out, use the fallback audio hint
  to determine the audio route to set

Change-Id: Ied8dcf00df9b2e3136c0ca2fdb7d006fee16c2dc
CRs-Fixed: 1043358
5 files changed