gpu-next: vaapi and vulkan don't work together on amd GFX8

Important Information

Provide following Information:

• mpv version: 0.35
• Linux Distribution and Version: Debian Sid
• Source of the mpv binary: apt
• If known which version of mpv introduced the problem: probably since gpu-next was added
• Window Manager and version: mutter 43.2 on Xorg
• GPU driver and version: mesa 22.3.4

Does not appear to be fixed in git.

Reproduction steps

Play a VAAPI-supported video with vo=gpu-next and gpu-api=vulkan

Expected behavior

VAAPI works.

Actual behavior

mpv checks for PL_HANDLE_DMA_BUF at https://github.com/mpv-player/mpv/blob/093db2f5650fd258621ceb5905cb62faa42cb52a/video/out/hwdec/dmabuf_interop_pl.c#L127 but libplacebo only provides this capability if GL is used (set in tex_handle_caps() at https://code.videolan.org/videolan/libplacebo/-/blob/master/src/opengl/gpu.c#L56). As a consequence VAAPI init fails and mpv falls back to vaapi-copy. GL works fine.

I am unsure if this is a libplacebo bug or if mpv is doing something wrong.

Log file

mpv.log

Start with video/out/hwdec/dmabuf_interop_pl.c at the PL_HANDLE_DMA_BUF check, then compare it with libplacebo's tex_handle_caps() behavior in the linked source. Reproduce with a VAAPI-supported video using vo=gpu-next and gpu-api=vulkan on AMD GFX8, and inspect the linked mpv.log. Done means VAAPI initializes and works without falling back to vaapi-copy.