python: Add error for creating abstact SimObjects

Currently, if you try to instantiate an abstract SimObject the error is
confusing and unhelpful.

"TypeError: _m5.param_<type>.<type>Params: No constructor defined!"

Now, it will instead say "Cannot instantiate an abstract SimObject"
and include the name of the object that causes the error.

Change-Id: Ia8c51e29dccd999ec90dcd39710cc91d9a5fb86f
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/59049
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/m5/SimObject.py

@@ -1175,6 +1175,8 @@ class SimObject(object, metaclass=MetaSimObject):
 
     # Call C++ to create C++ object corresponding to this object
     def createCCObject(self):
+        if self.abstract:
+            fatal(f"Cannot instantiate an abstract SimObject ({self.path()})")
         self.getCCParams()
         self.getCCObject() # force creation