making the repository REUSE compliant adding SPDX headers to files that 
have no copyright and licensing information

```
# SUMMARY

* Bad licenses:
* Deprecated licenses:
* Licenses without file extension:
* Missing licenses:
* Unused licenses:
* Used licenses: CC-BY-4.0, MIT
* Read errors: 0
* Files with copyright information: 12 / 12
* Files with license information: 12 / 12

Congratulations! Your project is compliant with version 3.0 of the REUSE Specification :-)
```

Signed-off-by: Francesco Pham <francesco.pham@huawei.com>