Provide an all codecs and an only-free codecs variant

At the moment we keep this overlay because we switch off video-codec=all build flag from Manjaro. I don't think we need to do this in general.

For some commercial projects it might make sense though. Therefore I propose we create a second package mesa-freeonly which is basically this package here (with the build flag removed) but also have the normal upstream Arch mesa package.

Thoughts?