ollama: allow `acceleration = "vulkan";`

Nixpkgs override allows `acceleration = vulkan;` which the home-manager
module seems to map. `vulkan` is also allowed as an value.

<https://github.com/NixOS/nixpkgs/blob/f13ff45afd1bb73e640eaa08a7066dbed07e3238/pkgs/by-name/ol/ollama/package.nix#L38>