decklink: Correctly set top-field-first/bottom-field-first

First of all, all the HD and UHD modes should be top-field-first, as
also returned by the Decklink mode iterator API.

Then we should include the caps field "field-order" in the caps of the
source (not the sink due to negotiation problems with optional fields).

And finally we should set the TFF flag on interlaced buffers that are
top-field-first.
4 files changed