MAINTAINERS: new entry for MPAM Driver

MAINTAINERS: new entry for MPAM Driver

Create a maintainer entry for the new MPAM Driver. Add myself and
James Morse as maintainers. James created the driver and I have
taken up the later versions of his series.

Cc: James Morse <james.morse@arm.com>
Reviewed-by: Shaopeng Tan <tan.shaopeng@jp.fujitsu.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Gavin Shan <gshan@redhat.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ben Horgan <ben.horgan@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>