[rbp/omxplayer] Remove flip timing logic from OMXPlayerVideo

The video is not rendered by the arm, so a lot of the page flipping code is redundant.
We just need to call flip periodically to get subtitles rendered and gui updated.
[rbp/omxplayer] Move buffering decision out of OMXPlayerAudio

This gets the m_stalled behaviour closer to dvdplayer which may help live tv issues.
The buffering will be re-added at a higher level from omxplayer
[rbp/omxplayer] Use OMXPlaySpeed for pause/resume
[rbp/omxplayer] Don't flush video when switching audio code

I believe whatever bug this was working around is no longer present
[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] Support frame advance (single step) with right arrow when paused