add basic support for Lenovo Thinkpad T440s (#83)

This adds basic support for the Thinkpad T440s, based on the work done for the T440p. The expression enables:

- microcode updates
- trackpoint support
- kernel module for battery level management

lenovo/thinkpad/t440s/default.nix

@@ -0,0 +1,14 @@
+{ config, lib, pkgs, ... }:
+
+{
+  imports = [
+    ../.
+    ../../../common/cpu/intel
+    ../../../common/pc/laptop/acpi_call.nix
+  ];
+
+  boot = {
+    # TODO: probably enable tcsd? Is this line necessary?
+    kernelModules = [ "tpm-rng" ];
+  };
+}