learning_gem5: Add config files for MSI protocol

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>