DTS modules (device modules) often have a single source file with an empty `struct Module`.
The module's yaml file now allows a `dts-only` boolean to be set, so the source file becomes optional.
`devicetree.yaml` is renamed everywhere to `module.yaml`
- Split up `gps-generic-module` into:
- `gps-generic-module` that contains only interfaces/configs/bindings (Apache license)
- `gps-meshtastic-module` that contains an implementation (GPL license)
- Update `LICENSE.md` for changes, but also added clarifications
- Added licenses to directories where they were missing
- Changed license of some test projects from GPL to Apache.
