refactor(nixos): move nvidia config to its own module

modules/nixos/hardware/gpu/default.nix

@@ -0,0 +1,41 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  inherit (lib)
+    mkMerge
+    mkIf
+    mkEnableOption
+    singleton
+    ;
+  cfg = config.hardware.gpu;
+in
+{
+  options.hardware.gpu = {
+    nvidia.enable = mkEnableOption "";
+  };
+  config = mkMerge [
+    (mkIf cfg.nvidia.enable {
+      hardware = {
+        graphics.enable = true;
+        graphics.extraPackages = singleton pkgs.nvidia-vaapi-driver;
+        nvidia.open = true;
+        nvidia.package = config.boot.kernelPackages.nvidiaPackages.latest;
+      };
+      services.xserver.videoDrivers = [ "nvidia" ];
+      nixpkgs.config.allowUnfree = true;
+      environment.variables = {
+        LIBVA_DRIVER_NAME = "nvidia";
+        __GLX_VENDOR_LIBRARY_NAME = "nvidia";
+        NVD_BACKEND = "direct";
+      };
+      nix.settings.substituters = [ "https://cuda-maintainers.cachix.org" ];
+      nix.settings.trusted-public-keys = [
+        "cuda-maintainers.cachix.org-1:0dq3bujKpuEPMCX6U4WylrUDZ9JyUG0VpVZa7CNfq5E="
+      ];
+    })
+  ];
+}