doc: release: migration guide: 3.6: add note on DT IRQ macros changes

  change is that this feature is rarely used and disabling it significantly reduces the memory

  footprint.

* For platforms that enabled :kconfig:option:`CONFIG_MULTI_LEVEL_INTERRUPTS`, the ``IRQ`` variant

  of the Devicetree macros now return the as-seen value in the devicetree instead of the Zephyr

  multilevel-encoded IRQ number. To get the IRQ number in Zephyr multilevel-encoded format, use

  ``IRQN`` variant instead. For example, consider the following devicetree:

  .. code-block:: devicetree

    plic: interrupt-controller@c000000 {

            riscv,max-priority = <7>;

            riscv,ndev = <1024>;

            reg = <0x0c000000 0x04000000>;

            interrupts-extended = <&hlic0 11>;

            interrupt-controller;

            compatible = "sifive,plic-1.0.0";

            #address-cells = <0x0>;

            #interrupt-cells = <0x2>;

    };

    uart0: uart@10000000 {

            interrupts = <10 1>;

            interrupt-parent = <&plic>;

            clock-frequency = <0x384000>;

            reg = <0x10000000 0x100>;

            compatible = "ns16550";

            reg-shift = <0>;

    };

  ``plic`` is a second level interrupt aggregator and ``uart0`` is a child of ``plic``.

  ``DT_IRQ_BY_IDX(DT_NODELABEL(uart0), 0, irq)`` will return ``10``

  (as-seen value in the devicetree), while ``DT_IRQN_BY_IDX(DT_NODELABEL(uart0), 0)`` will return

  ``(((10 + 1) << CONFIG_1ST_LEVEL_INTERRUPT_BITS) | 11)``.

  Drivers and applications that are supposed to work in multilevel-interrupt configurations should

  be updated to use the ``IRQN`` variant, i.e.:

  * ``DT_IRQ(node_id, irq)`` -> ``DT_IRQN(node_id)``

  * ``DT_IRQ_BY_IDX(node_id, idx, irq)`` -> ``DT_IRQN_BY_IDX(node_id, idx)``

  * ``DT_IRQ_BY_NAME(node_id, name, irq)`` -> ``DT_IRQN_BY_NAME(node_id, name)``

  * ``DT_INST_IRQ(inst, irq)`` -> ``DT_INST_IRQN(inst)``

  * ``DT_INST_IRQ_BY_IDX(inst, idx, irq)`` -> ``DT_INST_IRQN_BY_IDX(inst, idx)``

  * ``DT_INST_IRQ_BY_NAME(inst, name, irq)`` -> ``DT_INST_IRQN_BY_NAME(inst, name)``

Power Management

================