[rbp] Don't override dvdplayer with omxplayer.

Using dvdplayer can be useful on the Pi. We can actually play sd (up to 640x480 MPEG-4 video) video in real time.
This is useful for codec variants like DivX3 which we don't currently play.

This may expose bugs where dvdplayer is incorrectly used as the default player which will need to be fixed
[players] Use default players rather than hard coded DVDPlayer/PAPlayer
[rbp] Don't force dvdplayer for airplay
[rbp] Give plugins omxplayer when they request dvdplayer on pi
[PiSink] Fix some issues with buffering and multichannel
AE: add settings to enable ac3 transcode and upmix via ac3 transcoding
ActiveAE: implement settings for ac3 transcode and upmix
[rbp] Disable ac3transcode by default
[PiSink] More multichan/passthrough hacks
[rbp] Add hardware decode to dvdplayer

Hijack the abandoned OpenMaxVideo codec

Mostly working, but glitches/tearing visible
[omxcodec] Increase busy list to 2 to fix tearing