moved event_callback_t for compatibility with many drivers

Author: theotherjimmy

hal/api/Callback.h

@@ -873,6 +873,8 @@ class Callback<R()> {
     R (*_thunk)(void*, void*); 
 };
 
+ typedef Callback<void(int)> event_callback_t;
+
 
 } // namespace mbed
 

hal/api/FunctionPointer.h

@@ -56,7 +56,6 @@ class FunctionPointerArg1<R, void> : public Callback<R()> {
 };
 
 typedef FunctionPointerArg1<void, void> FunctionPointer;
-typedef FunctionPointerArg1<void, int> event_callback_t;
 
 
 } // namespace mbed