Our mailmap currently has 4 sections somehow documented.
Reorder few entries not related to "addresses from the original
git import" into the 3rd section, and add a comment to describe
it.

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Message-Id: <20190822230916.576-2-philmd@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>