boards/nucleo-h745zi: access CM4 core NSH over uart rpmsg

Command on the CM7 core:

  nsh-cm7> cu -l /dev/ttyproxy
  NuttShell (NSH) NuttX-10.4.0
  nsh-cm4>

Documentation/platforms/arm/stm32h7/boards/nucleo-h745zi/index.rst

@@ -14,6 +14,28 @@ The commands to build ``nsh_xxx_rptun`` configurations are as follows::
   cmake --build build_h7m7
   cmake --build build_h7m4
 
+Serial Console
+--------------
+
+The STLINK virtual console uses Serial Port 3 (USART3) with TX on PD8
+and RX on PD9 and is used by the Cortex-M7 core by default.
+
+================= ===
+VCOM Signal       Pin
+================= ===
+SERIAL_RX         PD9
+SERIAL_TX         PD8
+================= ===
+
+Access to the Cortex-M4 core can be acheived using an additional UART port
+or via RPMSG UART by setting ``CONFIG_RPMSG_UART_CONSOLE=y`` in CM4 configuration.
+
+If the RPMSG UART console is enabled, we can connect to it from CM7 using ``cu``::
+
+  nsh-cm7> cu -l /dev/ttyproxy
+  NuttShell (NSH) NuttX-10.4.0
+  nsh-cm4>
+
 Tools
 -----
 

boards/arm/stm32h7/nucleo-h745zi/configs/nsh_cm4_rptun/defconfig

@@ -37,6 +37,7 @@ CONFIG_RAM_SIZE=245760
 CONFIG_RAM_START=0x10000000
 CONFIG_RAW_BINARY=y
 CONFIG_RPMSG_UART=y
+CONFIG_RPMSG_UART_CONSOLE=y
 CONFIG_RPTUN=y
 CONFIG_RPTUN_PING=y
 CONFIG_RR_INTERVAL=200
@@ -44,6 +45,4 @@ CONFIG_SCHED_WAITPID=y
 CONFIG_START_DAY=6
 CONFIG_START_MONTH=12
 CONFIG_START_YEAR=2011
-CONFIG_STM32H7_USART1=y
 CONFIG_SYSTEM_NSH=y
-CONFIG_USART1_SERIAL_CONSOLE=y