Allow playback state update even when there is no metadata

* Separate metadata and playback state availabilities into two separate states
* Allow playback state update even if metadata received from MediaController is invalid
* This is because some MediaController don't provide metadata at all. The fluoride stack
  needs to update playback state even for this kind of MediaControllers.

Bug: 130278384
Test: manual
Change-Id: I2971892da39e1cd969d23cabd41ec109d83a7bea