irqchip/gic-v2m: Add support for multiple MSI frames

The GICv2m driver is so far limited to a single MSI frame, but
nothing prevents an implementation from having several of them.

This patch expands the driver to enumerate all frames, keeping
the first one as the canonical identifier for the MSI domains.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Tested-by: Duc Dang <dhdang@apm.com>
Cc: <linux-arm-kernel@lists.infradead.org>
Cc: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Link: http://lkml.kernel.org/r/1444822037-16983-3-git-send-email-marc.zyngier@arm.com


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>