util: Add the "sum" method to the java and lua m5 util wrappers.

util: Add the "sum" method to the java and lua m5 util wrappers.

Change-Id: Id55dec87af3e0fc89da6c5471a2aa02443063108
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/28175
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Pouya Fotouhi <pfotouhi@ucdavis.edu>
Maintainer: Gabe Black <gabe.black@gmail.com>