The pin control registers can have interrupts for example
for device wake-up. These interrupts can be treated as a
chained interrupt controller as suggested earlier by
Linus Walleij <linus.walleij@linaro.org>.

This patch adds support for interrupts in a way that
should be pretty generic, and works for the omaps that
support wake-up interrupts. On omaps, there's an
interrupt enable and interrupt status bit for each pin.
The two pinctrl domains on omaps share a single interrupt
from the PRM chained interrupt handler. Support for
other similar hardware should be easy to add.

Note that this patch does not attempt to handle the
wake-up interrupts automatically unlike the earlier
patches. This patch allows the device drivers to do
a request_irq() on the wake-up pins as needed. I'll
try to do also a separate generic patch for handling
the wake-up events automatically.

Also note that as this patch makes the pinctrl-single
an irq controller, the current bindings need some
extra trickery to use interrupts from two different
interrupt controllers for the same driver. So it
might be worth waiting a little on the patches
enabling the wake-up interrupts from drivers as there
should be a generic way to handle it coming. And also
there's been discussion of interrupts-extended binding
for using interrupts from multiple interrupt controllers.

In any case, this patch should be ready to go allowing
handling the wake-up interrupts in a generic way, or
separately from the device drivers.

Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: Prakash Manjunathappa <prakash.pm@ti.com>
Cc: Roger Quadros <rogerq@ti.com>
Cc: linux-kernel@vger.kernel.org
Cc: Benoît Cousson <bcousson@baylibre.com>
Cc: devicetree@vger.kernel.org
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Haojian Zhuang <haojian.zhuang@gmail.com>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>