[Chore] Clean up pytorch helper functions in vllm.utils (#26908)

Signed-off-by: Isotr0py <mozf@mail2.sysu.edu.cn>
Signed-off-by: isotr0py <2037008807@qq.com>

benchmarks/kernels/benchmark_reshape_and_cache_flash.py

@@ -12,9 +12,9 @@ from vllm.attention.ops.triton_reshape_and_cache_flash import (
 )
 from vllm.logger import init_logger
 from vllm.platforms import current_platform
-from vllm.utils import (
+from vllm.utils import FlexibleArgumentParser
+from vllm.utils.torch_utils import (
     STR_DTYPE_TO_TORCH_DTYPE,
-    FlexibleArgumentParser,
     create_kv_caches_with_random_flash,
 )