tracetool: include SPDX-License-Identifier in generated files

While these files are auto-generated, a later commit will add
reference output to git, so having SPDX-License-Identifier is
desirable.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Acked-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20250916081638.764020-5-berrange@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>