Some progress has been made on the USB core. The request set_address and get_descriptor are now recognized. The device_descriptor is successfully read by the PC. The Wireshark capture complies with the captured frame 

data-capture screenshot data is little endian

Wireshark screenshot

The captured frames screenshot is a raw bitstream with bit stuffing extraction. CRC is included. Octets are MSB first. The screenshot data capture is done on the ULX3S board using HDL4FPGA's ser_debug app. You can find the LatticeDiamond project file at https://github.com/hdl4fpga/hdl4fpga/blob/dev/boards/ULX3S/diamond/apps.ldf. The active implementation is ser_debug

USB core is now detected by Linux