Setup xserver in common and touchpad in lappy.

nodes/hosts/common/services/xserver.nix

@@ -0,0 +1,11 @@
+{ pkgs, ...}: {
+  # Enable the X11 windowing system.
+  # You can disable this if you're only using the Wayland session.
+  services.xserver = {
+    enable = true;
+    xkb = {
+      layout = "us";
+      variant = "";
+    };
+  };
+}