Fix gradient checkpointing + fp16 autocast for most models (#24247)

* fix gc bug

* continue PoC on OPT

* fixes

* 🤯

* fix tests

* remove pytest.mark

* fixup

* forward contrib credits from discussions

* forward contrib credits from discussions

* reverting changes on untouched files.

---------

Co-authored-by: zhaoqf123 <zhaoqf123@users.noreply.github.com>
Co-authored-by: 7eu7d7 <7eu7d7@users.noreply.github.com>

tests/models/clipseg/test_modeling_clipseg.py

@@ -202,6 +202,12 @@ class CLIPSegVisionModelTest(ModelTesterMixin, unittest.TestCase):
     def test_training_gradient_checkpointing(self):
         pass
 
+    @unittest.skip(
+        reason="The model does not support GC + autocast + fp16: https://github.com/huggingface/transformers/pull/24247"
+    )
+    def test_training_gradient_checkpointing_autocast(self):
+        pass
+
     @unittest.skip(reason="CLIPSegVisionModel has no base class and is not available in MODEL_MAPPING")
     def test_save_load_fast_init_from_base(self):
         pass
@@ -448,6 +454,12 @@ class CLIPSegModelTest(ModelTesterMixin, PipelineTesterMixin, unittest.TestCase)
     def test_hidden_states_output(self):
         pass
 
+    @unittest.skip(
+        reason="The model does not support GC + autocast + fp16: https://github.com/huggingface/transformers/pull/24247"
+    )
+    def test_training_gradient_checkpointing_autocast(self):
+        pass
+
     @unittest.skip(reason="Inputs_embeds is tested in individual model tests")
     def test_inputs_embeds(self):
         pass