README.license: Update to reflect SPDX tag usage

Update README.license since files now have SPDX tags rather than license
text. Adding a copy of BSD-2-Clause license since that no longer exists
within the project.

Signed-off-by: Rob Herring <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: David Gibson <[email protected]>
2 files changed