apple: add hid_apple.iso_layout=0 kernel param

In my experience, this makes keyboard behavior match letters printed
on it both on EU and US keyboards.

apple/default.nix

@@ -1,6 +1,10 @@
 { config, lib, ... }:
 
 {
+  boot.kernelParams = [
+    "hid_apple.iso_layout=0"
+  ];
+
   hardware.facetimehd.enable = lib.mkDefault
     (config.nixpkgs.config.allowUnfree or false);