[shardformer] support vision transformer (#4096)

* first v of vit shardformer

* keep vit

* update

* vit shard add vitattention vitlayer

* update num head shard para

* finish test for vit

* add new_model_class & postprocess

* add vit readme

* delete old files & fix the conflict

* fix sth

colossalai/shardformer/policies/bert.py

@@ -316,4 +316,4 @@ class BertForMultipleChoicePolicy(BertPolicy):
                                         ])
         }
         module_policy.update(addon_module)
-        return module_policy
+        return module_policy