Scrambling

[enjoy-digital]

USB3 scrambling is similar to SATA srambling, so LiteSATA scrambling code can be directly reused:
https://github.com/enjoy-digital/litesata/blob/master/litesata/core/link.py#L254-L337
https://github.com/enjoy-digital/litesata/blob/master/test/scrambler.c
https://github.com/enjoy-digital/litesata/blob/master/test/link_scrambler_tb.py

When implementing LiteSATA, lfsr_coefs were directly reused from the specification to speedup development. It would be good to improve that and be able to generate these coefficients directly from the polynom.

[enjoy-digital]

Scrambling is now implemented and tested against a USB3 Host. (https://github.com/enjoy-digital/usb3_pipe/blob/master/usb3_pipe/scrambling.py)