NuPlayer: Prevents creation of Video Decoder when we use Music Player

- Prevents instantion of Video Decoder when we use applications like
Music Player  which do not support Video Playback
- Adds a check to prevent scanning for sources when it is either an
Audio only clip or a video only clip or an AV clip played with a
Music Player.

Change-Id: I74dd9bc53e54fd4f3682536c987289ac252690b0
Signed-off-by: Arvind Thatikonda <arvindt@codeaurora.org>