Hi all,

This small series introduces SPDX tags to Xen:

1) add a mention to SPDX in CODING_STYLE
2) add a LICENSES directory with licenses and SPDX tags
3) adds the SPDX single-line comment to arch/arm/*.c

Note that arch/arm/*.c is just a start. Also, to make the changes as
mechanical as possible I restricted myself to:
- adding the single-line comment at the top of the file
- removing the copyright lines (when present) from the top of the file
  header

I purposedly restrained myself to do other cleanups to the headers: this
series already touches many files and I prefer to keep these changes as
mechanical as possible. Further improvements (style improvement,
removing what's left of the header, removing copyright lines, etc.) can
be done with subsequent patches more easily.

License changes are not intentional.

Cheers,

Stefano