JETSON TX2 PCIe configurations

How the PCIe configuration in Jetson TX2 is done in the SDK?
How can we change the default controller configuration 4x1, 1x1 to configuration to 1x1 1x1 1x1 configuration?
How to set PCI Gen configuration?

Please refer to TX2 adaptation guide. This kind of topics can also be searched in this forum too.