PCIe Gen2.0x16 or PCIe Gen3.0x16 support

[jixi2018]

Hi,

I used the latest RIFFA on my research project and it seems that the PCIe Gen2X8 BW was still too low(4GB/s). Just wonder if it is possible to modify the current source code to let RIFFA support PCIe Gen2.0X16(8GB/s) or PCIe Gen3.0X16(16GB/s)?

[alexforencich]

https://github.com/alexforencich/verilog-pcie / https://github.com/ucsdsysnet/corundum supports all the way up to gen 3 x16