stdlib: add SimPoint checkpoint generator

The previous SimPoint warmup length was limited by the gaps between
the starting instruction of one SimPoint and the ending instruction of
the SimPoint before it. This was to prevent duplicate SimPoints, but it
can significantly limit the warmup length.
In this commit, the warmup length limitation will be extended to the
starting instruction of one SimPoint regardless of the gap between
SimPoints.
A SimPoint checkpoint generator is created to help taking checkpoints
for SimPoints and make sure multiple SimPoint checkpoints are taken
when there are multiple SimPoints sharing the same starting instruction

Change-Id: If95f6813e8cbf5c01e41135c1b1bb91ed2e950ad
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/64351
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
4 files changed