Add EOS token

This PR adds the EOS token to the model configuration, as per the EOS token set in the tokenizer configuration. Some advanced generation modes in `.generate()` require the EOS token to be set :)

config.json

@@ -8,9 +8,9 @@
     "AutoModelForCausalLM": "modeling_phi.PhiForCausalLM"
   },
   "attention_dropout": 0.0,
-  "bos_token_id": null,
+  "bos_token_id": 50256,
   "embd_pdrop": 0.0,
-  "eos_token_id": null,
+  "eos_token_id": 50256,
   "hidden_act": "gelu_new",
   "hidden_size": 2560,
   "initializer_range": 0.02,