vo_gpu: vulkan: open DRM render fd when using VK_KHR_display

[philipl]

While the basic Vulkan Display context can theoretically drive the
display without the involvement of any non-Vulkan code, that prevents
us from using VAAPI acceleration. When initialising VAAPI without a
window system, we need to provide it with an opened DRM render fd
corresponding to the device to use.

In the context of using VK_KHR_display, that means we need to identify
which DRM device matches the selected Vulkan device, and then open its
render fd and set the necessary state that VAAPI expects to find.

With that done, the normal VAAPI<->Vulkan interop can kick in and we
get working acceleration

[Dudemanguy]

On AMD it picked vaapi-copy for me with hwdec=auto. That's the same thing the vulkan backend does on wayland for me so it works here at least.

[   0.124][v][vd] Requesting pixfmt 'vaapi_vld' from decoder.
[   0.125][d][ffmpeg/video] h264: Reinit context to 640x368, pix_fmt: vaapi_vld
[   0.158][i][vd] Using hardware decoding (vaapi-copy).

[philipl]

vaapi-copy always works. You need the open fd to be able to use the dmabuf passing.

[philipl]

@evelikov Thanks for the comments! Updated.

[evelikov]

Looking great, thanks o/