d3d12/va: Add AV1 encode support
This MR adds support for AV1 encode in the d3d12 gallium driver. There's a separate commit extending the frontend/va AV1 encode component to support some more parameters D3D12 supports.
For now, it requires DirectX Agility SDK preview 1.711.3. When libraries and hardware support requirements are met, a new entrypoint will light up in vainfo as below. Tested with cartwheel-ffmpeg.
vainfo: Supported profile and entrypoints
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VAProfileAV1Profile0 : VAEntrypointEncSlice
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