Add prototype system devicetree for nRF5340

That’s in nrf5340_system.dts, and is based on various related files in the zephyr tree. I sometimes left out some nodes where the upstream zephyr DTS doesn’t have them, but those are annotated with ‘skipped:’ comments. I also removed a bunch of node labels that would cause duplicates in a single file.

If you run run.sh, you’ll get two files: out-cpuapp.dts and out-cpunet.dts. These are the results of running lopper on nrf5340_system.dts to move the relevant cpu cluster to /cpus.

This is just meant as a starting point and sanity check that this SDT is acceptable to the tool. You can’t get zephyr to boot any target on this SoC with the results.

There are various hardcoded assumptions baked into this that encode a secure-only view of the world and should be followed up on. See ‘FIXME’ comments.