MAINTAINERS: Add our new mailing-list

We've been struggling to get an LF-hosted mailing list for a while, but
now that lists.linux.dev is there we opted in.

Let's add it to MAINTAINERS.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Jernej Skrabec <jernej.skrabec@siol.net>
Link: https://lore.kernel.org/r/20210331130830.64182-1-maxime@cerno.tech

Author: mripard

MAINTAINERS

@@ -1576,6 +1576,7 @@ R:	Jernej Skrabec <jernej.skrabec@siol.net>
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/sunxi/linux.git
+L:	linux-sunxi@lists.linux.dev
 F:	arch/arm/mach-sunxi/
 F:	arch/arm64/boot/dts/allwinner/
 F:	drivers/clk/sunxi-ng/