pinctrl: stmfx: Convert to immutable irq_chip

Convert the driver to immutable irq-chip with a bit of
intuition.

This driver rolls it's own resource handling and does not
use GPIOCHIP_IRQ_RESOURCE_HELPERS.

Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230403-immutable-irqchips-v1-8-503788a7f6e6@linaro.org