MAINTAINERS: Ondrej has moved

Update my email-address in MAINTAINERS to <megi@xff.cz>.  Also add
.mailmap entries to map my old, now blocked, email address.

Link: https://lkml.kernel.org/r/20231008105812.1084226-1-megi@xff.cz
Signed-off-by: Ondrej Jirman <megi@xff.cz>
Cc: Bjorn Andersson <quic_bjorande@quicinc.com>
Cc: Heiko Stuebner <heiko@sntech.de>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Konrad Dybcio <konrad.dybcio@linaro.org> # qcom
Cc: Mark Brown <broonie@kernel.org>
Cc: Qais Yousef <qyousef@layalina.io>
Cc: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>