irqchip: Add support for ARMv7-M NVIC

This interrupt controller is integrated in all Cortex-M3 and Cortex-M4
machines.

Support for this controller appeared in Catalin's Cortex tree based on
2.6.33 but was nearly completely rewritten.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Jonathan Austin <jonathan.austin@arm.com>
Cc: kernel@pengutronix.de
Link: http://lkml.kernel.org/r/1372231128-11802-1-git-send-email-u.kleine-koenig@pengutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>