🔨 FYSETC S6 small bootloader target (#22207)

Co-authored-by: Scott Lahteine <thinkyhead@users.noreply.github.com>

buildroot/share/PlatformIO/boards/marlin_fysetc_s6.json

@@ -21,7 +21,7 @@
   "name": "3D Printer control board",
   "upload": {
     "maximum_ram_size": 131072,
-    "maximum_size": 524288,
+    "maximum_size": 458752,
     "protocol": "stlink",
     "protocols": [
       "jlink",

buildroot/share/PlatformIO/boards/marlin_fysetc_s6_8000.json

@@ -0,0 +1,35 @@
+{
+  "build": {
+    "cpu": "cortex-m4",
+    "extra_flags": "-DSTM32F446xx",
+    "f_cpu": "180000000L",
+    "mcu": "stm32f446ret6",
+    "variant": "MARLIN_FYSETC_S6"
+  },
+  "connectivity": [
+    "can"
+  ],
+  "debug": {
+    "jlink_device": "STM32F446RE",
+    "openocd_target": "stm32f4x",
+    "svd_path": "STM32F446x.svd"
+  },
+  "frameworks": [
+    "arduino",
+    "stm32cube"
+  ],
+  "name": "3D Printer control board",
+  "upload": {
+    "maximum_ram_size": 131072,
+    "maximum_size": 491520,
+    "protocol": "stlink",
+    "protocols": [
+      "jlink",
+      "stlink",
+      "blackmagic",
+      "serial"
+    ]
+  },
+  "url": "https://www.st.com/en/microcontrollers-microprocessors/stm32f446.html",
+  "vendor": "FYSETC"
+}