p7zip: vendor debian patches

A few months ago I moved these patches to the new debian alsa instance [1], but
it looks like their `sha256`s on the tag at the remote have changed again.

It doesn't appear that debian's source remote is stable in the way we need it to
be; let's just vendor the patches to avoid future issues.

[1] https://github.com/NixOS/nixpkgs/pull/41769