MAINTAINERS: add irqchip related drivers to Marvell EBU maintainers

This commit updates the MAINTAINERS file so that the Marvell EBU
maintainers are also responsible for their irqchip drivers in
drivers/irqchip/.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>