stdlib,configs,tests: Examples of saving/restoring checkpoints

This change consists of two scripts,
- riscv-hello-save-checkpoint.py: runs the first million ticks of the
simulation and save a checkpoint.
- riscv-hello-load-checkpoint.py: loads the above checkpoint, and runs
the rest of the simulation.

This change also adds the two scripts as part of quick tests.

Change-Id: I7bd97ba953fab52f298cbbcf213f2ea5c185cc38
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/58829
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
3 files changed