MAINTAINERS, git-mailrc: Update sunxi maintainers

Maxime mentioned that he feels not having the time to be an Allwinner
maintainer anymore. Take over from him.

Maxime, many thanks for your great work in the past! I hope I can still
relay the occasional technical question to you in the future.

Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>