asus-fx506hm: use nvidia-open by default

[Andy3153]

Description of changes

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

Things done

• [x] Tested the changes in your own NixOS Configuration
• [x] Tested the changes end-to-end by using your fork of nixos-hardware and importing it via <nixos-hardware> or Flake input