webiste: Update tarball to aarch-system-20210904.tar.bz2

Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Change-Id: Ifee9a7ebe81ee88f4b23600ccf37fb2873434f34
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5-website/+/44327
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
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