Enable `throttled` for Thinkpad X1 gen 7 too

Even if this device is currently not mentioned upstream between the
devices that need this I stressed my machine (using `s-tui`) with and
without and I can confirm that it incremented the average CPU frequency
during the stress test (from 1.8/2GHz to around 3GHz).

lenovo/thinkpad/x1/7th-gen/default.nix

@@ -1,7 +1,10 @@
+{ lib, ... }:
 {
   imports = [
     ../.
     ../../../../common/pc/laptop/acpi_call.nix
     ../../../../common/pc/laptop/ssd
   ];
+
+  services.throttled.enable = lib.mkDefault true;
 }