media: v4l2: Trace calculated p/b0/b1 initial reflist

Add debug print statements to print the content of P & B reference
lists, to verify that the ordering of the generated reference lists is
correct. This is especially important for the field decoding mode,
where sorting is more complex.

Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Tested-by: Sebastian Fricke <sebastian.fricke@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>