doc: release-notes: add device model changes

  * Added :c:func:`k_realloc`, that uses kernel heap to implement traditional :c:func:`realloc`

    semantics.

  * Devices can now store devicetree metadata such as nodelabels by turning on

    :kconfig:option:`CONFIG_DEVICE_DT_METADATA`. This option may be useful in

    e.g. shells as devices can be obtained using human-friendly names thanks to

    APIs like :c:func:`device_get_by_dt_nodelabel`.

  * Any device initialization can be deferred if its associated devicetree node

    has the special ``zephyr,deferred-init`` property set. The device can be

    initialized later in time by using :c:func:`device_init`.

Bluetooth

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* Audio