MAINTAINERS: Add myself as maintainer for DRM Panels drivers

Add myself as co-maintainer for DRM Panel Drivers in order to help
reviewing and getting new panels drivers merged, and Remove Thierry
as he suggested since he wasn't active for a while.

Thanks Thierry for all your work!

Acked-by: Jagan Teki <jagan@amarulasolutions.com>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230216-topic-drm-panel-upstream-maintainance-v2-1-ffd262b72f16@linaro.org