Tools: enforce Values/Bitmask sanity check for vehicles as well as libraries

we have enforced this one-of-Values-or-Bitmask in libraries for a long time, and should have been enforcing it in vehicles before now.

MissionPlanner and MAVProxy ignore Values if Bitmask is present

Tools/autotest/param_metadata/param_parse.py

@@ -221,6 +221,10 @@ def process_vehicle(vehicle):
             else:
                 error("param: unknown parameter metadata field '%s'" % field[0])
 
+        if (getattr(p, 'Values', None) is not None and
+                getattr(p, 'Bitmask', None) is not None):
+            error("Both @Values and @Bitmask present")
+
         vehicle.params.append(p)
     current_file = None
     debug("Processed %u params" % len(vehicle.params))