mvc: Look up sps from both buffers
mvc: Do not try to parse ext slice yet

The sps management is still wrong, parsing seems mostly right.
h264: Refactor ff_h264_decode_ref_pic_list_reordering

In preparation for MVC support.

Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>
mvc: correctly implement this function
mvc: parse the mvc_ref_modification list
mvc: fix voidx
h264: restore explicit parsing of mvc nalus