Properly define on-board debug tools

Resolves platformio/platformio-docs#356

Author: valeros

Diff for: boards/uno_r4_wifi.json

@@ -29,6 +29,9 @@
     "variant": "UNOWIFIR4"
   },
   "debug": {
+    "default_tools": [
+      "cmsis-dap"
+    ],
     "onboard_tools": [
       "cmsis-dap"
     ],

Diff for: platform.py

@@ -156,6 +156,13 @@ def _add_default_debug_tools(self, board):
                     ],
                 }
 
+            debug["tools"][link]["onboard"] = link in debug.get(
+                "onboard_tools", []
+            )
+            debug["tools"][link]["default"] = link in debug.get(
+                "default_tools", []
+            )
+
         board.manifest["debug"] = debug
         return board