Support decoding and embedding VANC packets delivered via SMPTE 2038
into the SDI output.  We leverage an intermediate queue because
data packets are announced separately from video but we need to embed
the data into the video frame when it is output.

Note that this patch has some additional abstraction for data
streams in general as opposed to just SMPTE 2038 packets.  This is
because subsequent patches will introduce support for other
data codecs.

Thanks to Marton Balint for review/feedback.
Signed-off-by: Devin Heitmueller <dheitmueller@ltnglobal.com>
Signed-off-by: Marton Balint <cus@passwd.hu>