samples: ipm_mcux: update docs with lpc55s69

Updates .yaml and README with new boards support for lpcxpresso55s69.

Signed-off-by: Andrei Gansari <andrei.gansari@nxp.com>

samples/subsys/ipc/ipm_mcux/README.rst

@@ -6,23 +6,39 @@ Sample mailbox application
 Overview
 ********
 
-The :ref:`lpcxpresso54114` board has two core processors (Cortex-M4F
-and Cortex-M0+). This sample application uses a mailbox to send messages
-from one processor core to the other.
+Some NXP microcontrollers from LPC family are dual-core, this
+sample application uses a mailbox to send messages from one
+processor core to the other.
+
+This sample applies to the following boards:
+ -  :ref:`lpcxpresso54114`, two core processors (Cortex-M4F and Cortex-M0+)
+ -  :ref:`lpcxpresso55s69`, two core processors (dual Cortex-M33)
 
 Requirements
 ************
 
 - :ref:`lpcxpresso54114` board
+- :ref:`lpcxpresso55s69` board
 
-Building and Running
-********************
+Building the application for lpcxpresso54114_m4
+***********************************************
 
 .. zephyr-app-commands::
    :zephyr-app: samples/subsys/ipc/ipm_mcux
    :board: lpcxpresso54114_m4
    :goals: debug
 
+
+Building the application for lpcxpresso55s69_cpu0
+*************************************************
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/subsys/ipc/ipm_mcux
+   :board: lpcxpresso55s69_cpu0
+   :goals: debug
+
+Running
+*******
 Open a serial terminal (minicom, putty, etc.) and connect the board with the
 following settings:
 

samples/subsys/ipc/ipm_mcux/sample.yaml

@@ -4,7 +4,7 @@ sample:
     name: IPM MCUX Mailbox Sample
 tests:
     sample.ipc.ipm.ipm_mcux:
-        platform_allow: lpcxpresso54114_m4
+        platform_allow: lpcxpresso54114_m4 lpcxpresso55s69_cpu0
         tags: ipm
         harness: console
         harness_config: