SERDES bench file for LiteX Acron baseboard

[ohault]

Based on

• https://github.com/enjoy-digital/liteiclink/blob/master/bench/serdes/sqrl_acorn.py
• https://github.com/enjoy-digital/liteiclink/blob/master/bench/serdes/xcu1525.py

two benchmark scenarios could be targeted for LiteX Acron baseboard(s) with a single SFP DAC cable as interconnect.

1. SFP0 <-> SFP1 on a single LiteX Acron baseboard
2. SFP0 baseboard A <-> SFP0 baseboard B, between two LiteX Acorn basedboards

Similar two iperf, I wonder if a client/server architecture should not be considered.