This is a collection of changes needed to support V4L2 stateless decoders.
Note that I change the order of the duplicate_picture parameter to from the patch in !1011 so that it matches the order in VP9 decoder. I also made duplicate_picture required as when this is a keyframe it will populate the DPB. In this regard, the default implementation could cause major issues.
I've also added code to copy the original picture system_frame_number, as this ID is a unique identifier for the decoded image, having a different one on the new picture made no sense and was causing issues in V4L2 code, as it is used as an identifier in the kernel.