NuPlayer: Add support for non-streaming offload playback.

- Introduce mIsStreaming to identify non-streaming use case
  when setDataSourceAsync is called with valid fd.
- Call canOffloadStream with mIsStreaming instead of TRUE to
  support non-steaming compress offload playback.

Change-Id: Iecc0def40006c2c0884be6ea673185cce9883bb1
Conflicts:
media/libmediaplayerservice/nuplayer/NuPlayer.cpp
media/libmediaplayerservice/nuplayer/NuPlayer.h