doc: migrate-guide: Add nxp frdm_mcxa166 migrate information.

NXP frdm_mcxa166 is renamed to frdm_mcxa346, add this
information to migration-guide-4.3.rst.

Signed-off-by: Zhaoxiang Jin <[email protected]>

Author: ZhaoxiangJin

doc/releases/migration-guide-4.3.rst

@@ -29,6 +29,8 @@ Kernel
 Boards
 ******
 
+* NXP ``frdm_mcxa166`` is renamed to ``frdm_mcxa346``.
+
 Device Drivers and Devicetree
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