pinctrl: sx150x: use new nested IRQ infrastructure

Use the new gpiochip_irqchip_add_nested() and
gpiochip_set_nested_irqchip() calls to properly created
a nested irqchip and mark all child irqs properly with
their parent IRQ.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>