I made a GSX profile. Just drop the gsx.cfg file in the root of the aircraft.

C:\Program Files\Lockheed Martin\Prepar3D v4\SimObjects\Airplanes\CS_B777-200ER-II_GE90B

something like that.
I didn't change the water or lavatory values cause gsx doesn't support those yet. Door codes are all correct so it'll work with the animations panel. Let me know if there's any issues.
https://drive.google.com/open?id=1JL2j567SchCzRxNfH4ur0gRDiDwWjgRY