misc: Adding GitHub workflow files

This changes adds all of the workflows that will be run as we
move to using GitHub. It includes our compiler tests, our
nightly runs, and the continuous integration tests to be
run on every pull request.

Change-Id: I54c79aca7c0603337bd9fca443a0e2ffef603b0e
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/71298
Reviewed-by: Bobby Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Bobby Bruce <bbruce@ucdavis.edu>
3 files changed