ARM: at91/gpio: add .to_irq gpio_chip handler

Replace the gpio_to_irq() macro by a plain gpiolib .to_irq() handler.
This call is using the irqdomain to translate hardware to Linux
IRQ numbers.
The irq_to_gpio() macro is completely removed.

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