base, python, sim: Add support for resoving a stat using its name

base, python, sim: Add support for resoving a stat using its name

This CL adds resolve, a function in the Stats namespace that allows
access to a stat as specified by its name.

Change-Id: I4fa8bed394b4cb35d9c6cf5d8db062b8d6bb9ca5
Signed-off-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27891
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>