asus-fx506hm: use nvidia-open by default

Uses Nvidia open source kernel modules if driver version is higher than
555

Motivation:
1. Nvidia themselves will be using the open source kernel modules by
   default for drivers above version 555 and for boards that support it
   (like the one in this laptop)
2. this fixes kernel panics I've been having for months

asus/fx506hm/default.nix

@@ -1,4 +1,4 @@
-{ lib, ... }:
+{ config, lib, ... }:
 
 {
   imports =
@@ -14,6 +14,7 @@
   hardware.nvidia =
   {
     modesetting.enable = lib.mkDefault true;
+    open = lib.mkIf (lib.versionAtLeast config.hardware.nvidia.package.version "555") true;
 
     prime =
     {