pinctrl: sunxi: Declare the interrupt function for the A31

The primary pinctrl device has 4 interrupt banks. As usual, to be able to
generate interrupts, the pins supporting it need to be muxed to a special
function. Declare these functions in the pins array.
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>