MAINTAINERS: Mark the Nios II CPU as orphan

MAINTAINERS: Mark the Nios II CPU as orphan

Marek and Chris haven't been active for Nios II since years
(the last time seems to have been in 2017), and we've got
unhandled severe Nios II bug tickets in the bug tracker since
a long time, so to avoid wrong expectations of people who are
looking at the MAINTAINERS file, it's maybe best to mark the
Nios II entry as orphan nowadays.

Suggested-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230313183352.274744-1-thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Thomas Huth <thuth@redhat.com>