irqchip/bcm2835: Add support for being used as a second level controller

The BCM2836 (Raspberry Pi 2) uses two levels of interrupt handling
with the CPU-local interrupts being the root, so we need to register
ours as chained off of the CPU's local interrupt.

Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Cc: linux-rpi-kernel@lists.infradead.org
Cc: Lee Jones <lee@kernel.org>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: linux-arm-kernel@lists.infradead.org
Link: http://lkml.kernel.org/r/1438902033-31477-3-git-send-email-eric@anholt.net


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