configs: Use absolute import paths

Use absoluate import paths to be Python 3 compatible. This also
imports absolute_import from __future__ to ensure that Python 2.7
behaves the same way as Python 3.

Change-Id: Ica06ed95814e9cd3e768b3e1785075e36f6e56d0
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/16708
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

learning_gem5: Add config files for MSI protocol

Adds the required configuration files to run the MSI protocol. These
config files are much simpler than the current Ruby examples and follow
the pattern in the other Learning gem5 run scripts.

By default, this script runs with two CPUs and runs the recently added
thread test binary.

Currently, only SE mode is supported.

This code follows Learning gem5 Part 3.
http://learning.gem5.org/book/part3/index.html

Change-Id: I813a3153d49e47198444c38a6af30269bd1310cd
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/8943
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>