doc: releases: migration-guide: 4.4: mention mdio change

mention mdio change.

Signed-off-by: Fin Maaß <[email protected]>

Author: maass-hamburg

doc/releases/migration-guide-4.4.rst

@@ -32,6 +32,13 @@ Boards
 Device Drivers and Devicetree
 *****************************
 
+MDIO
+====
+
+* The ``mdio_bus_enable()`` and ``mdio_bus_disable()`` functions have been removed.
+  MDIO bus enabling/disabling is now handled internally by the MDIO drivers.
+  (:github:`99690`).
+
 QSPI
 ===