Enable loading with auto classes

This PR enables the model to be loaded with all `AutoModelForXxx` classes supported in `modeling_RW.py`

config.json

@@ -7,6 +7,10 @@
   "attention_dropout": 0.0,
   "auto_map": {
     "AutoConfig": "configuration_RW.RWConfig",
+    "AutoModel": "modelling_RW.RWModel",
+    "AutoModelForSequenceClassification": "modelling_RW.RWForSequenceClassification",
+    "AutoModelForTokenClassification": "modelling_RW.RWForTokenClassification",
+    "AutoModelForQuestionAnswering": "modelling_RW.RWForQuestionAnswering",
     "AutoModelForCausalLM": "modelling_RW.RWForCausalLM"
   },
   "bias": false,