[rbp/omxplayer] Avoid audio codec when in passthrough modes

There is no need to open the ffmpeg audio codec when in passthrough mode.
Also there is no need to close/open the OMXAudio component when parameters (like number of channels) change in passthough.
This avoids an unpleasant stutter
Merge pull request #3212 from popcornmix/avoid_audio_codec

[rbp/omxplayer] Avoid audio codec when in passthrough modes