Summary:

Test with pytorch#3399 and this command passes 
```
python -m examples.models.llama2.export_llama -kv --mps
```
Without this diff, it will error out
```
in _verify_exported_program_signature
    raise SpecViolationError(
torch._export.verifier.SpecViolationError: Buffer output getitem_1 does not point to a buffer that exists.
Dict of buffers that are mutated, in order: {'getitem_1': 'layers_0_attention_SDPA_kv_cache_k_cache', 'getitem': 'layers_0_attention_SDPA_kv_cache_v_cache', 'getitem_3': 'layers_1_attention_SDPA_kv_cache_k_cache', 'getitem_2': 'layers_1_attention_SDPA_kv_cache_v_cache', 'getitem_5': 'layers_2_attention_SDPA_kv_cache_k_cache', 'getitem_4': 'layers_2_attention_SDPA_kv_cache_v_cache', 'getitem_7': 'layers_3_attention_SDPA_kv_cache_k_cache', 'getitem_6': 'layers_3_attention_SDPA_kv_cache_v_cache', 'getitem_9': 'layers_4_attention_SDPA_kv_cache_k_cache', 'getitem_8': 'layers_4_attention_SDPA_kv_cache_v_cache'}
Buffer nodes available: []
```
The root cause is that by `is_parameter`, it tags all data including mutable buffers.

Reviewed By: larryliu0820

Differential Revision: D56941763