mbedtls: use correct SPDX License Identifier and add License file
License "GPL-2.0+" is deprecated License Identifier according to
SPDX License list [1]. The correct one is GPL-2.0-or-later.
While at it, also add the License file.
[1] https://spdx.org/licenses/
Signed-off-by: Josef Schlehofer <[email protected]>
Josef Schlehofer