Add CI

[rossburton]

We need some CI. At least, verification that the layer parses.

[rossburton]

https://github.com/rossburton/meta-acrn/tree/azure is a pretty basic proof of concept. No building, just parse and dry-run for master and warrior.

[rossburton]

CC @moto-timo. If we want to build in CI then I think we'll either need a CI system that lets us share a sstate-cache or host the runner ourself.

[rossburton]

I've a prototype using GitHub Actions at https://github.com/rossburton/meta-acrn/tree/actions but we don't have actions enabled on the intel group.