gpio: dln2: Use irqchip template

This makes the driver use the irqchip template to assign
properties to the gpio_irq_chip instead of using the
explicit calls to gpiochip_irqchip_add(). The irqchip is
instead added while adding the gpiochip.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Daniel Baluta <daniel.baluta@gmail.com>
Cc: Daniel Baluta <daniel.baluta@gmail.com>
Cc: Octavian Purdila <octavian.purdila@nxp.com>
Link: https://lore.kernel.org/r/20200722073426.38890-1-linus.walleij@linaro.org