ulysses mpu: additional api (#7649)

It looks like `save_checkpoint` expects `get_model_parallel_*` API in
the `mpu` object. So adding it to the Ulysses slim mpu version.

This solves this problem in HF Trainer:
```
[rank1]:   File "/code/users/stas/github/transformers-alst-integration/src/transformers/trainer.py", line 3248, in _save_optimizer_and_scheduler
[rank1]:     self.model_wrapped.save_checkpoint(output_dir)
[rank1]:   File "/code/users/stas/github/DeepSpeed/deepspeed/runtime/engine.py", line 3497, in save_checkpoint
[rank1]:     self._save_checkpoint(save_dir,
[rank1]:   File "/code/users/stas/github/DeepSpeed/deepspeed/runtime/engine.py", line 3709, in _save_checkpoint
[rank1]:     save_path = self._get_ckpt_name(save_dir, tag)
[rank1]:                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[rank1]:   File "/code/users/stas/github/DeepSpeed/deepspeed/runtime/engine.py", line 3039, in _get_ckpt_name
[rank1]:     mp_rank = 0 if self.mpu is None else self.mpu.get_model_parallel_rank()
[rank1]:                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
[rank1]: AttributeError: module 'deepspeed.runtime.sequence_parallel.parallel_state_sp' has no attribute 'get_model_parallel_rank'. Did you mean: 'get_sequence_parallel_rank'?
```

Signed-off-by: Stas Bekman <[email protected]>

Author: stas00

deepspeed/runtime/sequence_parallel/parallel_state_sp.py

@@ -88,3 +88,9 @@ def get_sequence_parallel_rank():
 def get_sequence_data_parallel_rank():
     """Return my rank for the sequence data parallel group."""
     return dist.get_rank(group=get_sequence_data_parallel_group())
+
+
+# since we only have 1 additional dimension over DP, we can just alias MP with SP
+get_model_parallel_rank = get_sequence_parallel_rank
+get_model_parallel_world_size = get_sequence_parallel_world_size
+get_model_parallel_group = get_sequence_parallel_group