ARM: dts: OMAP3+: Correct gpio #interrupts-cells property

The OMAP gpio binding documention [1] states that the #interrupts-cells
property for gpio controllers should be 2. Currently, for OMAP3+ devices
the #interrupt-cells is set to 1. By setting this property to 2, it
allows clients to pass a 2nd parameter indicating the sensitivity (level
or edge) and polarity (high or low) of the interrupt. The OMAP gpio
controllers support these options and so update the #interrupt-cells
property for OMAP3+ devices to 2.

[1] Documentation/devicetree/bindings/gpio/gpio-omap.txt

Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Benoit Cousson <benoit.cousson@linaro.org>