base-stats,python: Update PyBind11 ScalarInfo fields to readonly

This change keeps the ScalarInfo class consistent with the other Info
classes exposed via PyBind11.

Change-Id: I4d420d509e4654de844e75f58aeaaf67109775d3
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/41693
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed