Add DCO 1.1 file
Add DCO 1.1 file

All contributions to this document are made under the Developer
Certificate of Origin process. Contributers must include a
"Signed-off-by" line in their commit text indicating that their change
can be redistributed under the project's license.

Signed-off-by: Grant Likely <9069e6f5a2b566e2674a0ba1e2bf39c12c195fad@linaro.org>

devicetree-org/devicetree-specification,kvekaria/devicetree-specification