default value for services.hardware.openrgb.motherboard

[lucasew]

Description of changes

With this PR if something references the common processor module so that OpenRGB works out of the box if enabled.

Things done

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

[lucasew]

Tested

[Mic92]

Since this is a bit of a niche application, what do you think about inverting the control and set it in the openrbg module instead? NixOS/nixpkgs#253048

[lucasew]

Since this is a bit of a niche application, what do you think about inverting the control and set it in the openrbg module instead? NixOS/nixpkgs#253048

Awesome idea.