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

I switched to consistently using irqd_to_hwirq() consistently
while we are at it.

As the driver now needs to get the gpio_chip in the .irq_mask
and .irq_unmask callbacks, I switched to a pattern where we
first fetch the gpio_chip and then the state container from
that in two steps. The compiler will do the same thing anyway.

Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20230403-immutable-irqchips-v1-9-503788a7f6e6@linaro.org