This "interlaced" data layout - what does it mean exactly? Does it just mean
fields in separate surfaces or is there anything else going on additionally? I
couldn't find any docs on this in mesa.

Since we can do weaving on the Kodi side anyway (for VDPAU), would it be enough
to add flags, say VA_EXPORT_SURFACE_TOP_FIELD and
VA_EXPORT_SURFACE_BOTTOM_FIELD, to vaExportSurfaceHandle? Would that then be
roughly equivalent to what we get with VDPAURegisterVideoSurfaceNV?