vpu: encoder: h264: add idr-interval property
vpu: encoder: add slice-size and intra-refresh properties
vpu: encoder: mark mpeg4 and h264 output as parsed

... which it is coming out of an encoder and is needed for
succesful negotiation into vpu decoder.
Merge pull request #10 from mnauw/vpuenc-enhancements

Misc vpuenc enhancements