doc: release-notes: PM related release notes

Add PM release notes.

Signed-off-by: Flavio Ceolin <[email protected]>

Author: Flavio Ceolin

doc/releases/release-notes-3.4.rst

@@ -1370,6 +1370,10 @@ Libraries / Subsystems
     that will wake the system up in the future. This can be used to influence
     the system on which low power states can be used.
 
+  * Added a new device tree property ``zephyr,pm-device-runtime-auto`` to
+    automatically enable device runtime power management on a device after its
+    initialization.
+
 HALs
 ****