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 <stas@stason.org>
