gpio: tc3589x: use gpiolib irqchip helpers

Now that the gpiolib irqchip helpers can support nested, threaded
IRQ handlers, switch the TC3589x driver over to using this new
infrastructure. Tested on the Ux500.

Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>