demos: add NXP reference board page

Refer issue 38: #38
Address review comment:
NXP i.MX8M Plus is also supported.

Author: Sipke Vriend

demos/reference_boards.rst

@@ -12,4 +12,5 @@ In general the OpenAMP feature being exemplified is found in the `OpenAMP source
    docker_images
    system_reference-AMD-Xilinx
    system_reference-ST
+   system_reference-NXP
    inter_process

demos/rpmsg_multi_services.rst

@@ -157,3 +157,7 @@ This RPMsg Multi Services Sample is demonstrated in the following reference impl
 
    * Refer to `Zephyr Build Instructions <https://github.com/OpenAMP/openamp-system-reference/tree/main/examples/zephyr/rpmsg_multi_services>`_.
    * Refer to `example demo script <https://github.com/OpenAMP/openamp-demo/blob/main/demos/demo-stm32mp157c-dk2/my-extra-stuff/home/root/demo1>`_.
+
+* :ref:`NXP <reference_board_NXP>`
+
+   * Refer to Application Note `AN13970 Running Zephyr RTOS <https://www.nxp.com/docs/en/application-note/AN13970.pdf>`_

demos/system_reference-NXP.rst

@@ -0,0 +1,13 @@
+
+
+.. _reference_board_NXP:
+
+====================
+NXP Reference Boards
+====================
+
+A number of the `OpenAMP project examples <https://github.com/OpenAMP/openamp-system-reference/tree/main/examples>`_ can be executed on NXP Reference boards.
+
+* NXP `8MPLUSLPD4-EVK <https://www.nxp.com/design/design-center/development-boards-and-designs/8MPLUSLPD4-EVK>`_.
+
+The `AN13970 Running Zephyr RTOS on Cadence Tensilica HiFi 4 DSP <https://www.nxp.com/docs/en/application-note/AN13970.pdf>`_ application note provides instructions for setting up the evaluation board.