media: uapi: Add H264 low-level decoder API compound controls.

Stateless video codecs will require both the H264 metadata and slices in
order to be able to decode frames.

This introduces the definitions for the structures used to pass the
metadata from the userspace to the kernel.

[hverkuil-cisco@xs4all.nl: add space after . in ".For"]
[hverkuil-cisco@xs4all.nl: sync v4l2_ctrl_h264_decode_params struct layout with header]

Co-developed-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Signed-off-by: Pawel Osciak <posciak@chromium.org>
Signed-off-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>