doc: Add a new migration guide entry to clock

Add the following property renaming entries to
the migration:
* freqs_mhz
* cg_reg
* pll_ctrl_reg

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

Author: rruuaanng

doc/releases/migration-guide-4.1.rst

@@ -140,6 +140,12 @@ ADC
 
 * Renamed the ``compatible`` from ``nxp,kinetis-adc12`` to :dtcompatible:`nxp,adc12`.
 
+Clock
+=====
+* Renamed the devicetree property ``freqs_mhz`` to ``freqs-mhz``.
+* Renamed the devicetree property ``cg_reg`` to ``cg-reg``.
+* Renamed the devicetree property ``pll_ctrl_reg`` to ``pll-ctrl-reg``.
+
 Counter
 =======