pinctrl: at91: don't use the same irqchip with multiple gpiochips

Sharing the same irqchip with multiple gpiochips is not a good
practice. For instance, when installing hooks, we change the state
of the irqchip. The initial state of the irqchip for the second
gpiochip to register is then disrupted.

Signed-off-by: Ludovic Desroches <ludovic.desroches@microchip.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>