[Cin] add Vulkan hwaccel

[Andrea paz]

Thank you, just these days I'm testing with the “configure” flags;
your patches happen right.
In CinHV, Adam had put an option in the rendering window to write an
ffmpeg command directly, without going through presets. An option that
opens you a terminal (or a simple input window, as Adam did), makes
you use external ffmpeg, and then the result falls back into the
rendering window configuration would not be bad. This would get around
the problem with the filter graph and using multiple streams that
prevent some plugins from working. Do you think this is possible by
copying Adam's commit?