website: update tutorial to reflect portname changes and code needed to work with V21

Change-Id: I3938fee1f9bad31c6df8e3ceb65ca254eba5f3cc
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/44545
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
2 files changed