doc: Add a new migration guide entry to DAC

Rename the voltage_reference and power_down_mode
properties to voltage-reference and power-down-mode
in the devicetree and bindings of the DAC subsystem.

Signed-off-by: James Roy <[email protected]>

Author: rruuaanng

doc/releases/migration-guide-4.1.rst

@@ -157,6 +157,12 @@ Display
 * Renamed the devicetree propertys ``pclk_pol`` and ``data_cmd-gpios``
   to ``pclk-pol`` and ``data-cmd-gpios``.
 
+DAC
+===
+
+* Renamed the devicetree properties ``voltage_reference`` and ``power_down_mode``
+  to ``voltage-reference`` and ``power-down-mode``.
+
 Enhanced Serial Peripheral Interface (eSPI)
 ===========================================