[Feature] Enable PP + SP for llama (#5868)

* fix cross-PP-stage position id length diff bug

* fix typo

* fix typo

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* use a one cross entropy func for all shardformer models

---------

Co-authored-by: Edenzzzz <wtan45@wisc.edu>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

colossalai/shardformer/policies/llama.py

@@ -1,4 +1,3 @@
-import warnings
 from functools import partial
 from typing import Callable, Dict, List, Union
 
@@ -66,13 +65,6 @@ class LlamaPolicy(Policy):
         else:
             norm_cls = RMSNorm
 
-        if self.pipeline_stage_manager is not None:
-            self.shard_config.enable_sequence_parallelism = False
-            self.shard_config.enable_sequence_overlap = False
-            self.shard_config.sequence_parallelism_mode = None
-            warnings.warn(
-                f"For llama, sequence parallelism is currently not compatible with pipeline parallelism, set to be False"
-            )
         sp_mode = self.shard_config.sequence_parallelism_mode or None
         sp_size = self.shard_config.sequence_parallel_size or None
         sp_group = self.shard_config.sequence_parallel_process_group or None