framework/av: Fix AudioFlinger create track failure

- AudioFlinger track creation fails after mediaserver crash
- Mediaplayer doesn't register for new sessionId value if
  mediaserver crashes during a song switch of music player
  and it uses the old sessionId though sessionId values are
  reset by AudioFlinger.
  AudioFlinger assigns the same sessionId to Tone Generator
  and since strategies of these two session differ it would
  result in track creation failure.
- Fix this issue by registering for new sessionId for
  mediaplayer if mediaserver crashes in idle state

Change-Id: Icc8d204bec5d2fa97db17a7319904baa29115b19