NuPlayer: Use a software renderer when using software codecs

This mimics what is done in AwesomePlayer and MediaCodec -
ideally this logic perhaps should be moved into ACodec to
avoid having to replicate it in every caller.

This makes HLS and RTSP playback work in the emulator.

Change-Id: I18027dc3e469889baaae3e1c4afb559de7d0f7d3