[rbp/omxplayer] Remove unused state from OMXClock

m_has_audio/m_has_video are always set before OMXReset is called, so just make them local parameters.
m_video_start and m_audio_start are unused, so remove them.

This commit should have no functional change
[ffmpeg] Add armv6 optimised path to dts decode
[rbp/omxplayer] Support frame advance (single step) with right arrow when paused
[rbp/omxplayer] Do we need discontinuity handling?

So far I've not seen what this is needed for and it does cause problems for some files.
[rbp/omxplayer] Support ff/rew