nuplayer: Synchronize video and audio decoders configuration

  Video decoder configuration takes more time than audio
decoder configuration and happens in two different threads
leads to buffer transactions of audio much earlier than video
which results in frame drops in the start of playback. Hence
synchronize both decoders configuration.

Change-Id: Iabc1267c9c70b0e87e0c9043633d2d9ad7548a29
CRs-Fixed: 774777