NuPlayer: add implementations of suspend/resume APIs

- API:suspend() will just pause the player and release all the decoders
  to replace reset() which will release the whole player
- API:resume() will just init the decoders again, then start() will be
  called to start to play the streaming

CRs-Fixed: 587059
Change-Id: Ib57625109ea993dc0ae6f298386d09c807d42455