MAINTAINERS: add maintainer of simpletrace.py

MAINTAINERS: add maintainer of simpletrace.py

In my work to refactor simpletrace.py, I noticed that there's no
maintainer of it, and has the status of "odd fixes". I'm using it from
time to time, so I'd like to maintain the script.

I've added myself as reviewer under "Tracing" to be informed of changes
that might affect simpletrace.py.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Mads Ynddal <m.ynddal@samsung.com>
Message-id: 20230926103436.25700-14-mads@ynddal.dk
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>