docs: Provide info on extra support provided by the Raspberry Pi 4 integration

Signed-off-by: Andrei Gherzan <andrei.gherzan@huawei.com>

docs/hardware-support/boards/index.rst

@@ -18,4 +18,5 @@ This section details the boards supported as part of |main_project_name|.
    seco-imx8mm-c61
    seco-px30-d23
    raspberrypi4
-   arduino-nano-33-ble
\ No newline at end of file
+   raspberrypi-armv8
+   arduino-nano-33-ble

docs/hardware-support/boards/raspberrypi-armv8.rst

+.. SPDX-FileCopyrightText: Huawei Inc.
+..
+.. SPDX-License-Identifier: CC-BY-4.0
+
+.. include:: ../../definitions.rst
+
+.. _raspberrypi-armv8:
+
+Raspberry Pi ARMv8 (64 bit)
+###########################
+
+.. contents::
+   :depth: 3
+
+Overview
+********
+
+The platform adds explicit support for Raspberry Pi 4 boards in 64-bit mode.
+You can read more about that support in :ref:`raspberrypi`.
+
+While doing so, the |main_project_name| integration provides extra support on
+the same image for other 64-bit, ARMv8, capable Raspberry Pi boards. For
+example, an image generated for Raspberry Pi 4 will work as well on a Raspberry
+Pi 3 (in 64 bit mode). You can check more details of the 64-bit support in the
+official Raspberry Pi `documentation
+<https://www.raspberrypi.com/documentation/computers/config_txt.html#arm_64bit>`_.