MAINTAINERS: Update entry for MediaTek SoC support

MAINTAINERS: Update entry for MediaTek SoC support

The linux-mediatek IRC channel has moved to liber.chat for quite some
time. Apart from that, not all patches are also send to LKML, so add
this ML explicitly.

And last but not least:
Angelo does a wunderfull job in reviewing patches for all kind of
devices from MediaTek.

Cc: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>
Link: https://lore.kernel.org/r/20230201152256.19514-1-matthias.bgg@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>