docs: migration-guide-4.2: Add note about Renesas RA4M1 migration

* Zephyr now supports version 1.11.1 of the :zephyr:board:`neorv32`.

* ``arduino_uno_r4_minima``, ``arduino_uno_r4_wifi``, and ``mikroe_clicker_ra4m1`` have migrated to

  new FSP-based configurations.

  While there are no major functional changes, the device tree structure has been significantly revised.

  The following device tree bindings are now removed:

  ``renesas,ra-gpio``, ``renesas,ra-uart-sci``, ``renesas,ra-pinctrl``,

  ``renesas,ra-clock-generation-circuit``, and ``renesas,ra-interrupt-controller-unit``.

  Instead, use the following replacements:

  - :dtcompatible:`renesas,ra-gpio-ioport`

  - :dtcompatible:`renesas,ra-sci-uart`

  - :dtcompatible:`renesas,ra-pinctrl-pfs`

  - :dtcompatible:`renesas,ra-cgc-pclk-block`

Device Drivers and Devicetree

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