[Cin] add Vulkan hwaccel

[Andrea paz]

> We have problem on input side, where hw decoding does not cooperate with filters ....

Maybe I didn't understand the problem: I thought that Hw acceleration
in timeline is only about playback. I believe that filters are not
accelerated even with standalone ffmpeg. In fact, there are few
filters built specifically for vulkan; are these the ones that don't
work for you?
During my tests I had managed to compile CinGG with the filters for
vulkan (it seems to me with a simple: “export FFMPEG_EXTRA_CFG=
--enable-vulkan”), but these did not work due to the classic errors
("input/Output error", "invalid argument", etc).

PS: among other tests, I failed to compile opencv (system) and opencl.
I have yet to try frei0r, lensfun and lcms2...