multimedia/libva-nvidia-driver: add new port
This is an VA-API implementation that uses NVDEC as a backend. This
implementation is specifically designed to be used by Firefox for
accelerated decode of web content, and may not operate correctly in
other applications.
System requirements:
- Non-legacy NVIDIA GPU
- nvidia-drm-kmod for DMA-BUF
- libc6-shim (nv-sglrun) for NVDEC