Fix #1591 ffmpeg 8 error: init_hw_device for hwupload with VAAPI

[FrostKiwi]

This fixes #1591 and NixOS/nixpkgs#473008 by extension.

With the release of FFMPEG 8, hwupload (a ffmpeg feature which is used by memories' VAAPI (AMD GPU) Hardware video decode) requires a device to be specified via init_hw_device. This is documented by the ffmpeg project here: https://trac.ffmpeg.org/wiki/Hardware/VAAPI#DeviceSelection

Where filters require a device (for example, the hwupload filter), the device used in a filter graph can be specified with the -filter_hw_device option:

ffmpeg -init_hw_device vaapi=foo:/dev/dri/renderD128 -i ... -filter_hw_device foo -filter_complex > ...hwupload... ...

Right now, FFMPEG 8 + Memories + VAAPI AMD GPU Hardware decode errors out with [hwupload @ 0x558ab089cd40] A hardware device reference is required to upload frames to.

With FFMPEG 7 this was not required (the documentation has the word can, not must) and was initialized automatically, but with the release of FFMPEG 8 this became required. I am not sure why and started an inquiry in the FFMPEG-DEVEL mailing list: https://lists.ffmpeg.org/archives/list/ffmpeg-devel@ffmpeg.org/thread/BZF2EO2WGL6U52WAKFPOKNT53OJF2AYG/

Anyhow, this PR makes memories follow the documentation and initialize the VAAPI device explicitly.