ARM: mvebu: link PCIe controllers to the MSI controller

This commit adjusts the Armada 370 and Armada XP PCIe controllers
Device Tree informations to reference their MSI controller. In the
case of this platform, the MSI controller is implemented by the MPIC.

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