pinctrl: at91: Use generic irq_{request,release}_resources()

The at91-specific irq_{request,release}_resources() callbacks are
identical to the generic ones, modulo the bug fix in 5b76e79c
("gpiolib: irqchip: prevent driver unloading if gpio is used as irq
only").

Until commit 8b67a1f0

 ("gpio: don't override irq_*_resources()
callbacks"), the buggy at91-specific callbacks were never used, though.

Hence drop the at91-specific ones in favor of the generic ones.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>