[rbp/omxplayer] Add plumbing for audio GetCacheTotal
[rbp/omxplayer] OMX spec says we can transition from execute to idle
[rbp/omxplayer] We don't require this for command line omxplayer
[rbp/omxplayer] Add calls for stepping and retreiving the clock adjustment
[rbp/omxplayer] Use OMXPlaySpeed for pause/resume
[rbp/omxplayer] dispmanx now handles negative rectangles correctly so adjustment not required