Configure the virtio net device on arm as well. For this, we need to update the FDT builder to support adding virtio block devices, and update the unit tests such that they work on arm as well.

The definition of done for this task is to:

• make it possible to configure one virtio net
• add tests to validate that this configuration work (we should be able to reuse the existing tests from x86_64)

Out of scope:

• the end to end integration test is out of scope because it requires extensive changes to the S3 bucket & the way we're building the test resources. Any changes that are required once we have a test image should be part of that PR instead. Handled in Linux image for testing aarch64 #218