SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.
Avoids dragging in IniFile, EXI device and SI device headers in this header which is
quite widely used throughout the codebase.
This also uncovered a few cases where indirect inclusions were being
relied upon, which this also fixes.