gpio: siox: Convert to immutable irq_chip

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

In this case I had to figure out a way to get to the
struct gpio_chip that would work even when the irq_chip
is not part of the driver state container. I did this by
just doing what most other GPIO drivers do and pass
the state struct as data to devm_gpiochip_add_data()
and rewrite accordingly.

Cc: Marc Zyngier <maz@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>