avid: include precharge in phys timecode calculation
avid: include precharge in phys timecode calculation

Precharge results in the SourceClip in the MaterialPackage referencing
position 'precharge' in the file SourcePackage. This offset needs to
be taken into account when converting a timecode at the top of package chain
to an offset to the physical SourcePackage at the bottom.

Limecraft/ebu-bmx,Limecraft/ebu-bmx,Limecraft/ebu-bmx