Add XAVC LongGOP support for DCI 4K (not just UHD)

Add XAVC LongGOP support (422/10BPP) for DCI 4K (as for UHD 3840) - MainConcept supports it already but no plugin option exists.  

The larger Intra codec is fine for some purposed but not all.  Going out to other tools for delivery when the LongGOP is needed at DCI  isn't ideal.