Lighting support hardcoded to 1 light

Currently, we use `GX_SetChanCtrl` in our tev shaders, which controls the which lights will be used to render the upcoming objects.
However, which lights are active is decided by our rendering system, and the scene.
This means that if there are no lights in a scene, but the shader requires 3, things will break horribly.

Find a good solution for this.