gpio: pca953x: 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_nested() and
gpiochip_set_nested_irqchip(). The irqchip is instead
added while adding the gpiochip.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Marek Vasut <marek.vasut@gmail.com>
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Adam Ford <aford173@gmail.com>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20200717144040.63253-1-linus.walleij@linaro.org