Add a CRC on the 4Gbps GEM trigger links
This merge request adds an 8-bits CRC on the 4Gbps GEM trigger links in order to discard as many invalid clusters as possible. Some of the work in based on sorted, rebased, cleaned up, and tested commits from !146.
More context and details can be found in #60 (closed) (and #50 (closed)). Fixes #60 (closed).
Tested on a GE1/1 test stand and deployed at P5.
Edited by Laurent Petre