website: added RISCV to the valid ISAs list

Change-Id: Ief7746d2bf65cd119dd223b96027d825cc2cb481
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/52343
Reviewed-by: Bobby R. Bruce <bbruce@ucdavis.edu>
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: Bobby R. Bruce <bbruce@ucdavis.edu>
1 file changed