Segregate lenovo/ subdir into thinkpad and ideapad directories

There are several significant differences between ThinkPads and the
other Lenovo models, so this structure must be more precise

lenovo/thinkpad/general.nix

@@ -0,0 +1,18 @@
+{ lib, ... }:
+
+with lib;
+
+{
+  hardware.trackpoint = mkDefault {
+    enable = true;
+    emulateWheel = true;
+  };
+
+  hardware.enableAllFirmware = true;
+  services.tlp.enable = true;
+
+  services.xserver = {
+    synaptics.enable = false;
+    libinput.enable = true;
+  };
+}