release_notes: Add section about utilities

Add information about UTIL_LISTIFY deprecation.

Signed-off-by: Krzysztof Chruscinski <[email protected]>

Author: nordic-krch

doc/releases/release-notes-3.1.rst

@@ -143,6 +143,10 @@ Deprecated in this release
     ``_usec`` set functions have been deprecated. Other units can be specified
     using, e.g. ``PWM_USEC()`` macros, which convert down to nanoseconds.
 
+* Utilities
+
+  * :c:macro:`UTIL_LISTIFY` has been deprecated. Use :c:macro:`LISTIFY` instead.
+
 Stable API changes in this release
 ==================================