pinctrl: nomadik: don't default-flag IRQs as falling

There is no point in adding any default trigger for these
GPIO interrupts: the device tree should contain all trigger
information and the platforms using the driver boots
exclusively from device tree.

Also the boot log is nagging me to fix this:

[    0.771057] ------------[ cut here ]------------
[    0.775695] WARNING: CPU: 0 PID: 1 at
   ../drivers/gpio/gpiolib.c:1622 _gpiochip_irqchip_add+0x138/0x160
[    0.785034] /soc/gpio@8012e000: Ignoring 2 default trigger
(...)
[    0.942962] gpio 8012e000.gpio: at address e08f8000
(etc ad nauseam)

Suggested-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>