Documentation: Add documentation to arc-socket-grid

Signed-off-by: Alan C. Assis <acassis@gmail.com>

Documentation/platforms/arm/imxrt/boards/arcx-socket-grid/index.rst

@@ -0,0 +1,92 @@
+================
+ARCX Socket Grid
+================
+
+The ARCX Socket Grid is an industrial board from ARCX. This boards uses the i.MX RT1052 crossover MCU with ARM Cortex M7 core.
+
+.. figure:: arc_socket_grid.jpg
+   :align: center
+
+Features
+========
+
+- Processor
+    - MIMXRT1052DVL6A processor
+- Memory
+    - 256 Mb SDRAM memory
+    - 512 Mb Hyper Flash
+- Connectivity
+    - USB host and OTG connectors
+    - Ethernet (10/100T) connector
+    - CAN transceivers
+    - I/O-Link interfaces
+    - 4-20mA interface
+    - Sensors for voltage, current, temperature, etc
+
+Serial Console
+==============
+
+The serial console is available through pins:
+
+========= ============= ==========
+UART1_TXD GPIO_AD_B0_12 LPUART1_TX
+UART1_RXD GPIO_AD_B0_13 LPUART1_RX
+========= ============= ==========
+
+LEDs and buttons
+================
+
+LEDs
+----
+
+There are three LED status indicators located on the Board.  The
+functions of these LEDs include:
+
+==== =============
+Pin  Description
+==== =============
+LED1  Power Supply
+LED2  User LED
+LED3  5V Power ON
+==== =============
+
+Only a single LED (LED2) is under software control.  It connects to
+GPIO_AD_B0_08.
+
+This LED is not used by the board port unless CONFIG_ARCH_LEDS is
+defined.  In that case, the usage by the board port is defined in
+include/board.h and src/imxrt_autoleds.c. The LED is used to encode
+OS-related events as follows:
+
+================ ======================= =====
+SYMBOL           Meaning                 LED
+================ ======================= =====
+LED_STARTED      NuttX has been started  OFF
+LED_HEAPALLOCATE Heap has been allocated OFF
+LED_IRQSENABLED  Interrupts enabled      OFF
+LED_STACKCREATED Idle stack created      ON
+LED_INIRQ        In an interrupt         N/C
+LED_SIGNAL       In a signal handler     N/C
+LED_ASSERTION    An assertion failed     N/C
+LED_PANIC        The system has crashed  FLASH
+================ ======================= =====
+
+Thus if the LED is statically on, NuttX has successfully  booted and is,
+apparently, running normally.  If the LED is flashing at approximately
+2Hz, then a fatal error has been detected and the system has halted.
+
+Buttons
+-------
+
+There are no buttons in the Board:
+
+Configurations
+==============
+
+nsh
+---
+    
+Configures the NuttShell (nsh) located at examples/nsh.  This NSH
+configuration is focused on low level, command-line driver testing.
+Built-in applications are supported, but none are enabled.  This
+configuration does not support a network.