irqchip/armada-370-xp: Enable MSI-X support

irqchip/armada-370-xp: Enable MSI-X support

Armada XP does not only support MSI, but also MSI-X. This patch sets
the MSI_FLAG_PCI_MSIX flag in the interrupt controller driver which
is the only change necessary to enable MSI-X support on this SoC. As
the Linux PCI MSI-X infrastructure takes care of writing the data and
address structures into the BAR specified by the MSI-X controller.

Signed-off-by: Stefan Roese <sr@denx.de>
Reviewed-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Gregory CLEMENT <gregory.clement@free-electrons.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>