Add SPDX-License-Identifier line to each source file that
contains license text. More details about SPDX license identifiers
can be found at [1].
The scancode-toolkit [2] was used to match license text to the correct
SPDX-License-Identifier:
$ scancode --license --copyright --html scancode_result.html ./
[1] https://spdx.org/licenses/
[2] https://github.com/nexB/scancode-toolkit
Signed-off-by: Igor Opaniuk <igor.opaniuk@oss.qualcomm.com>