irqchip: Add support for TI-NSPIRE irqchip

This patch adds support for the interrupt controllers found in some
TI-Nspire models.

FIQ support was taken out to simplify the driver code and may be added
in later. Since Linux on this platform doesn't really use FIQs, this
wasn't really that important in the first place.

[ tglx: Made zevio_handle_irq static and reordered __init functions ]

Signed-off-by: Daniel Tang <dt.tangr@gmail.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
Link: http://lkml.kernel.org/r/1386223937-12189-1-git-send-email-dt.tangr@gmail.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>