doc: release-notes: mention new cmake DT extensions

Mention some new devicetree helpers and changes to existing ones.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

doc/releases/release-notes-3.0.rst

@@ -287,6 +287,21 @@ USB
 Build and Infrastructure
 ************************
 
+* Build system
+
+  * New CMake extension functions:
+
+    * ``dt_alias()``
+    * ``target_sources_if_dt_node()``
+
+  * The following CMake extension functions now handle devicetree aliases:
+
+    * ``dt_node_exists()``
+    * ``dt_node_has_status()``
+    * ``dt_prop()``
+    * ``dt_num_regs()``
+    * ``dt_reg_addr()``
+    * ``dt_reg_size()``
 
 * Devicetree