feat(boards): add m5stack-atoms3u board (#172)

* feat(boards): add m5stack-atoms3u board matches pindefs PR espressif/arduino-esp32#11352

Author: mhaberler

boards/m5stack-atoms3u.json

@@ -0,0 +1,42 @@
+{
+  "build": {
+    "arduino": {
+      "memory_type": "qio_opi",
+      "partitions": "default_8MB.csv"
+    },
+    "core": "esp32",
+    "extra_flags": [
+      "-DARDUINO_M5Stack_ATOMS3U",
+      "-DARDUINO_USB_MODE=1",
+      "-DARDUINO_USB_CDC_ON_BOOT=1",
+      "-DARDUINO_RUNNING_CORE=1",
+      "-DARDUINO_EVENT_RUNNING_CORE=1"
+    ],
+    "f_cpu": "240000000L",
+    "f_flash": "80000000L",
+    "flash_mode": "dio",
+    "mcu": "esp32s3",
+    "variant": "m5stack_atoms3"
+  },
+  "connectivity": [
+    "bluetooth",
+    "wifi"
+  ],
+  "debug": {
+    "openocd_target": "esp32s3.cfg"
+  },
+  "frameworks": [
+    "arduino",
+    "espidf"
+  ],
+  "name": "M5Stack AtomS3U",
+  "upload": {
+    "flash_size": "8MB",
+    "maximum_ram_size": 327680,
+    "maximum_size": 8388608,
+    "require_upload_port": true,
+    "speed": 460800
+  },
+  "url": "https://docs.m5stack.com/en/core/AtomS3U",
+  "vendor": "M5Stack"
+}