MAINTAINERS: Name and email address change

I have changed my name and email address.  Update the MAINTAINERS file
to match, and .mailmap in case anyone wants to send me an email because
of some past commit I authored.  (As suggested by Philippe, I put the
.mailmap line into the "preferred name forms" section, considering it
counts as a git author config change.)

Signed-off-by: Hanna Reitz <hreitz@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>