vulkan video decoding: anv status update

After hacking the Intel media-driver and ffmpeg I managed to work out how the anv hardware mostly works now for h264 decoding.

I've pushed a branch [1] and a MR[2] to mesa. The basics of h264 decoding are working great on gen9 and compatible hardware. I've tested it on my one Lenovo WhiskeyLake laptop.

I have ported the code to hasvk as well, and once we get moving on this I'll polish that up and check we can h264 decode on IVB/HSW devices.

The one feature I know is missing is status reporting, radv can't support that from what I can work out due to firmware, but anv should be able to so I might dig into that a bit.

[1] https://gitlab.freedesktop.org/airlied/mesa/-/tree/anv-vulkan-video-decode

[2] https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20782

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