pinctrl/at91: Don't provide a default trigger type

at91 used to set a default trigger type for GPIO interrupts in
order to cope with the old board files. These days are long gone,
and it all gets probed through DT.

Andras Szemzo reported that the Ethernet device on his board was
bailing to be probed, due to a conflict in interrupt trigger.
Surely enough, this is due to this default trigger still being
present, and turning this into a IRQ_TYPE_NONE fixes the issue.

Reported-by: Andras Szemzo <szemzo.andras@gmail.com>
Tested-by: Andras Szemzo <szemzo.andras@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>