Migrate to SPDX-FileCopyrightText notices

Migrate to SPDX-FileCopyrightText notices

Automated using the following snippet:

find . \
  \( -name '*.c' -o -name '*.cpp' -o -name '*.h' -o -name '*.hpp' \
     -o -name '*.py' -o -name '*.sh' \) -print0 |
while IFS= read -r -d '' file; do
  sed -E -i \
    's/Copyright(\s*\(C\))?\s+([0-9]{4})\s+(.*)/SPDX-FileCopyrightText: \2 \3/g' \
    "$file"
done

Change-Id: I9a12cdc7fc8bed0c6436b5be62cc57f56ec4ed89
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>