ARM: at91/snapper9260: move gpio_to_irq out of structure initialization

gpio_to_irq() implementation will be moved from a macro to a
plain function: we cannot use it in a structure initialization
anymore.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Reviewed-by: Ryan Mallon <rmallon@gmail.com>