esp32/boards: Add M5STACK_ATOM board definition.

ATOM is a very small ESP32 development board produced by M5Stack, with a
size of 24mm * 24mm, with peripherals such as WS2812, IR, button, MPU6886
(Only Matrix), and 8 GPIO extensions.  It also has a plastic shell.

ports/esp32/boards/M5STACK_ATOM/manifest.py

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+include("$(PORT_DIR)/boards/manifest.py")
+freeze("modules")

ports/esp32/boards/M5STACK_ATOM/modules/atom.py

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+# M5Stack ATOM MicroPython Helper Library
+# MIT license; Copyright (c) 2021 IAMLIUBO work for M5STACK
+#
+# Hardware details:
+#       ATOM Lite    https://docs.m5stack.com/en/core/atom_lite
+#       ATOM Matrix  https://docs.m5stack.com/en/core/atom_matrix
+
+from micropython import const
+from machine import Pin
+import neopixel
+
+# M5STACK ATOM Hardware Pin Assignments
+"""
+          FRONT
+                  |3V3|
+|G21|   IR   G12  |G22|
+|G25|   BTN  G39  |G19|
+| 5V| WS2812  G27 |G23|
+|GNG| MPU G21 G25 |G33|
+     G32 G26 5V GND
+       Grove Port
+"""
+
+# WS2812
+WS2812_PIN = const(27)
+
+# Button
+BUTTON_PIN = const(39)
+
+# IR
+IR_PIN = const(12)
+
+# I2C
+I2C0_SCL_PIN = const(21)
+I2C0_SDA_PIN = const(25)
+
+# Grove port
+GROVE_PORT_PIN = (const(26), const(32))
+
+
+class ATOM:
+    def __init__(self, np_n):
+        self._np = neopixel.NeoPixel(pin=Pin(WS2812_PIN), n=np_n)
+        self._btn = Pin(BUTTON_PIN, Pin.IN, Pin.PULL_UP)
+
+    def get_button_status(self):
+        return self._btn.value()
+
+    def set_button_callback(self, cb):
+        self._btn.irq(trigger=Pin.IRQ_FALLING, handler=cb)
+
+    def set_pixel_color(self, num, r, g, b):
+        if num <= self._np.n:
+            self._np[num] = [r, g, b]
+            self._np.write()
+
+    def get_pixel_color(self, num):
+        if num <= self._np.n:
+            return self._np[num]
+
+    def set_pixels_color(self, r, g, b):
+        self._np.fill([r, g, b])
+        self._np.write()
+
+
+class Lite(ATOM):
+    # WS2812 number: 1
+    def __init__(self):
+        super(Lite, self).__init__(np_n=1)
+
+
+class Matrix(ATOM):
+    # WS2812 number: 25
+    def __init__(self):
+        super(Matrix, self).__init__(np_n=25)

ports/esp32/boards/M5STACK_ATOM/mpconfigboard.cmake

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+set(SDKCONFIG_DEFAULTS
+    boards/sdkconfig.base
+    boards/sdkconfig.ble
+    boards/sdkconfig.240mhz
+    boards/M5STACK_ATOM/sdkconfig.board
+)
+
+if(NOT MICROPY_FROZEN_MANIFEST)
+    set(MICROPY_FROZEN_MANIFEST ${MICROPY_BOARD_DIR}/manifest.py)
+endif()

ports/esp32/boards/M5STACK_ATOM/mpconfigboard.h

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+#define MICROPY_HW_BOARD_NAME "M5Stack ATOM"
+#define MICROPY_HW_MCU_NAME "ESP32-PICO-D4"

ports/esp32/boards/M5STACK_ATOM/sdkconfig.board

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+CONFIG_FLASHMODE_QIO=y
+CONFIG_ESPTOOLPY_FLASHFREQ_80M=y
+CONFIG_SPIRAM_SPEED_80M=y
+CONFIG_ESP32_REV_MIN_1=y
+CONFIG_LWIP_LOCAL_HOSTNAME="M5StackATOM"