This allows to turn on/off all hw implementations for a specific video codec across the tree. Patent encumbered codecs can cause problems for distributions due to the nature of at least MPEG-LA licensing.
https://jina-liu.medium.com/settle-your-questions-about-h-264-license-cost-once-and-for-all-hopefully-a058c2149256 is probably the best explaination I can find.
From a distro pov, codec fees are a jigsaw puzzle, you only seem to become a problem when you fit all the pieces.
This patch will allow disabling the mesa piece of the puzzle.