LibGL+LibSoftGPU: Add GL_MAX_LIGHTS to get_context_parameter

This is required to allow lighting to work properly in the GL. We
currently have the maximum number of lights in the software GL context
set to 8, as this is the minimum that OpenGL mandates according to the
spec.

Userland/Libraries/LibSoftGPU/DeviceInfo.h

@@ -14,6 +14,7 @@ struct DeviceInfo final {
     String vendor_name;
     String device_name;
     unsigned num_texture_units;
+    unsigned num_lights;
 };
 
 }