media: h264: Sort p/b reflist using frame_num

In the reference list builder, frame_num refers to FrameNumWrap
in the spec, which is the same as the pic_num for frame decoding.
The same applies for long_term_pic_num and long_term_frame_idx.

Sort all type of references by frame_num so the sort can be reused
for fields reflist were the sorting is done using frame_num instead.
In short, pic_num is never actually used for building reference
lists.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Sebastian Fricke <sebastian.fricke@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>