typedefs: Separate incomplete types and function types

While there, rewrite the obsolete file comment.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20190812052359.30071-12-armbru@redhat.com>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
[File comment rewritten, commit message adjusted]
1 file changed