FDT access from a driver during attach

[Vincent DEFERT <vincent.defert%posteo.net@localhost>]

I want to add interrupt handling to the Meson pinctrl driver.
I have seen that this is handled by attaching gpioirq to the desired pin 
with gpioctl(8) and there's an example of how to implement the 
underlying capability in sunxi_gpio.c.
I also have the S905 documentation and the source code of the vendor 
Linux driver as reference. So far, so good.

The only thing I don't know is how to retrieve the GPIO interrupt 
controller configuration.
It is stored in a gpio_intc node with the "amlogic,meson-gpio-intc" 
compatible string, but none of the 2 gpio instances reference it.
How can I search the full FDT to find this node?