Feed forward chunking others (#6365)

* Feed forward chunking for Distilbert & Albert

* Added ff chunking for many other models

* Change model signature

* Added chunking for XLM

* Cleaned up by removing some variables.

* remove test_chunking flag

Co-authored-by: patrickvonplaten <patrick.v.platen@gmail.com>

src/transformers/configuration_utils.py

@@ -191,6 +191,7 @@ class PretrainedConfig(object):
         self.pad_token_id = kwargs.pop("pad_token_id", None)
         self.eos_token_id = kwargs.pop("eos_token_id", None)
         self.decoder_start_token_id = kwargs.pop("decoder_start_token_id", None)
+        self.chunk_size_feed_forward = kwargs.pop("chunk_size_feed_forwar", 0)
 
         # task specific arguments
         self.task_specific_params = kwargs.pop("task_specific_params", None)