doc: releases: 4.2: mention pm_device_driver_deinit()

Mention introduction of pm_device_driver_deinit() in the 4.2 release
notes.

Signed-off-by: Bjarki Arge Andreasen <bjarki.andreasen@nordicsemi.no>

Author: bjarki-andreasen

doc/releases/release-notes-4.2.rst

@@ -221,6 +221,7 @@ New APIs and options
     * :kconfig:option:`CONFIG_PM_DEVICE_RUNTIME_DEDICATED_WQ_PRIO`
     * :kconfig:option:`CONFIG_PM_DEVICE_RUNTIME_DEDICATED_WQ_INIT_PRIO`
     * :kconfig:option:`CONFIG_PM_DEVICE_RUNTIME_ASYNC`
+    * :c:func:`pm_device_driver_deinit`
 
   * Sockets