website: CHI protocol documentation

Documentation for the new CHI protocol.

JIRA: https://gem5.atlassian.net/browse/GEM5-908
Change-Id: I9ae25c1e252717bf77dfa77129b91d0c9cead2e1
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/43063
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
13 files changed