vulkan video encoding: radv update

After the video decode stuff was fairly nailed down, Lynne from ffmpeg nerdsniped^Wtalked me into looking at h264 encoding.

The AMD VCN encoder engine is a very different interface to the decode engine and required a lot of code porting from the radeon vaapi driver. Prior to Xmas I burned a few days on typing that all in, and yesterday I finished typing and moved to debugging the pile of trash I'd just typed in.

Lynne meanwhile had written the initial ffmpeg side implementation, and today we threw them at each other, and polished off a lot of sharp edges. We were rewarded with valid encoded frames.

The code at this point is only doing I-frame encoding, we will work on P/B frames when we get a chance.

There are also a bunch of hacks and workarounds for API/hw mismatches, that I need to consult with Vulkan spec and AMD teams about, but we have a good starting point to move forward from. I'll also be offline for a few days on holidays so I'm not sure it will get much further until mid January.

My branch is [1]. Lynne ffmpeg branch is [2].

[1] https://gitlab.freedesktop.org/airlied/mesa/-/commits/radv-vulkan-video-enc-wip

[2] https://github.com/cyanreg/FFmpeg/tree/vulkan_decode

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