AVRCP: Fix deadlock between Avrcp.this and mMediaPlayerInfoList

* addMediaPlayerInfo (acquires mMediaPlayerInfoList)
  -> updateCurrentController (acquires Avrcp.this)
* onSessionDestroyed (acquires Avrcp.this)
  -> removeMediaController (acquires mMediaPlayerInfoList)
* Above is a deadlock that causes ANR
* This CL moves updateCurrentController call out of the critical section
  in addMediaPlayerInfo to resolve this deadlock situation

Bug: 63458678
Test: make, test connecting to Avrcp devices
Change-Id: Iaae2d1bc005a181b950d4306d0773332f6c1afef