irqchip/stm32-exti: Map interrupts through interrupts-extended

The mapping of EXTI events to its parent interrupt controller is both SoC
and instance dependent.

The current implementation requires adding a new mapping table to the
driver's code and a new compatible for each new EXTI instance.

Check for the presence of the optional interrupts-extended property and use
it to map EXTI events to the parent's interrupts.

For old device trees without the optional interrupts-extended property, the
driver's behavior is unchanged, thus keeps backward compatibility.

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240415134926.1254428-4-antonio.borneo@foss.st.com