stdlib: Introduce an ARM Board

This changes adds a new board to the gem5 stdlib, which is capable
of simulating an ARM based full system. It also adds an example
config script to perform a boot-test using an Ubuntu 18.04 disk
image. A test has been added in the gem5-library-example for the
same.

Change-Id: Ic95ee56084a444c7f1cf21cdcbf40585dcf5274a
Signed-off-by: Kaustav Goswami <kggoswami@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/58910
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
6 files changed