NuPlayer: Fix for PCM offload fallback on BT

 -Start the Decoded PCM offload playback on speaker or headset and
  connect BT, audio is not played on BT.
 -During tear down event on BT connection, instantiation of decoder
  is initated before actual shut down of decoder completes.So
  decoder is not getting instantiated again after tear down event.
  It is a race condition between instantiation of Decoder and
  shut down of decoder.
 -Defer the instantiation of decoder in intermediate state

CRs-Fixed: 916643, 829392
Change-Id: Ic346cb7bb7b1babe21618daa8f8746c00f4b61b3