made features a first class citizen

hal/targets.json

@@ -6,6 +6,7 @@
         "extra_labels": [],
         "is_disk_virtual": false,
         "macros": [],
+        "features": [],
         "detect_code": [],
         "public": false
     },

workspace_tools/toolchains/__init__.py

@@ -298,11 +298,7 @@ class mbedToolchain:
 
             # Add target's symbols
             self.symbols += self.target.macros
-            # Add target's hardware
-            try :
             self.symbols += ["DEVICE_" + feature + "=1" for feature in self.target.features]
-            except AttributeError :
-                pass
             # Add extra symbols passed via 'macros' parameter
             self.symbols += self.macros