gpio: pcf857x: Switch to use gpiolib irqchip helpers

gpio: pcf857x: Switch to use gpiolib irqchip helpers

Switch the PCF857x GPIO driver to use the gpiolib irqchip helpers.
This driver uses a nested threaded interrupt, hence handle_nested_irq()
and gpiochip_set_chained_irqchip() must be used.

Note that this removes the checks added in commit 21fd3cd1874a2ac8
("gpio: pcf857x: call the gpio user handler iff gpio_to_irq is done"),
as the interrupt mappings are no longer created on-demand by the driver,
but by gpiochip_irqchip_add() during initialization.

Signed-off-by: Geert Uytterhoeven <[email protected]>
Signed-off-by: Linus Walleij <[email protected]>