irqchip: Add support for MOXA ART SoCs

This patch adds an irqchip driver for the main interrupt controller
found on MOXA ART SoCs.

Signed-off-by: Jonas Jensen <jonas.jensen@gmail.com>
Cc: grant.likely@secretlab.ca
Cc: thomas.petazzoni@free-electrons.com
Cc: arnd@arndb.de
Cc: u.kleine-koenig@pengutronix.de
Cc: linux@arm.linux.org.uk
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1372941531-6393-1-git-send-email-jonas.jensen@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>