replace flash method with openocd, disable automatic stack sizing

targets/feather-stm32f405.json

@@ -1,6 +1,8 @@
 {
   "inherits": ["cortex-m4"],
   "build-tags": ["feather_stm32f405", "stm32f405", "stm32f4", "stm32"],
+  "automatic-stack-size": false,
+  "default-stack-size": 1024,
   "cflags": [
     "-Qunused-arguments"
   ],
@@ -8,6 +10,7 @@
   "extra-files": [
     "src/device/stm32/stm32f405.s"
   ],
-  "flash-method": "command",
-  "flash-command": "dfu-util -a 0 --dfuse-address 0x08000000 -D {hex}"
+  "openocd-transport": "swd",
+  "openocd-interface": "jlink",
+  "openocd-target": "stm32f4x"
 }