irqchip: GICv3: ITS: MSI support

Now, the bit of code that allow us to use the ITS as a MSI controller.
Both MSI and MSI-X are supported.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Link: https://lkml.kernel.org/r/1416839720-18400-10-git-send-email-marc.zyngier@arm.com


Signed-off-by: Jason Cooper <jason@lakedaemon.net>
Git-commit: b48ac83d6bbc20a973c3e8133fd1ebda873d026a
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Puja Gupta <pujag@codeaurora.org>