media: uapi: h264: Get rid of the p0/b0/b1 ref-lists

Those lists can be extracted from the dpb, let's simplify userspace
life and build that list kernel-side (generic helpers will be provided
for drivers that need this list).

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Reviewed-by: Ezequiel Garcia <ezequiel@collabora.com>
Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Tested-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>