treewide: restructure modules

make every module contain config attribute
and if module doesn't use module arguments,
don't make it a function

nix-os/virtualization.nix

@@ -2,15 +2,17 @@
 { lib, config, pkgs, ... }:
 
 {
-  #virtualisation.waydroid.enable = true;
-  programs.virt-manager.enable = true;
-  virtualisation.libvirtd = {
-    enable = true;
-    qemu.ovmf = {
+  config = {
+    #virtualisation.waydroid.enable = true;
+    programs.virt-manager.enable = true;
+    virtualisation.libvirtd = {
       enable = true;
-      packages = [
-        pkgs.OVMFFull.fd
-      ];
+      qemu.ovmf = {
+        enable = true;
+        packages = [
+          pkgs.OVMFFull.fd
+        ];
+      };
     };
   };
 }