MAINTAINERS: Add mailing list for Realtek SoCs

Document linux-realtek-soc mailing list to be CC'ed on patches.

Signed-off-by: Andreas Färber <afaerber@suse.de>

MAINTAINERS

@@ -2160,6 +2160,7 @@ F:	Documentation/devicetree/bindings/timer/rda,8810pl-timer.txt
 ARM/REALTEK ARCHITECTURE
 M:	Andreas Färber <afaerber@suse.de>
 L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
+L:	linux-realtek-soc@lists.infradead.org (moderated for non-subscribers)
 S:	Maintained
 F:	arch/arm64/boot/dts/realtek/
 F:	Documentation/devicetree/bindings/arm/realtek.yaml