MAINTAINERS: kgdb: Add myself as a reviewer for kgdb/kdb

I'm interested in kdb / kgdb and have sent various fixes over the
years.  I'd like to get CCed on patches so I can be aware of them and
also help review.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://lore.kernel.org/r/20190920104404.1.I237e68e8825e2d6ac26f8e847f521fe2fcc3705a@changeid
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>