pinctrl: pic32: Convert to immutable irq_chip

Convert the driver to immutable irq-chip with a bit of
intuition. Switch some call to use irqd_to_hwirq() in the
process.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230414-immutable-irqchips-2-v1-1-6b59a5186b00@linaro.org