Add pt_load_map_location to allow loading to cuda (#16869)

Signed-off-by: Jerry Zhang <jerryzh168@gmail.com>

vllm/config.py

@@ -1564,6 +1564,16 @@ class LoadConfig:
     use_tqdm_on_load: bool = True
     """Whether to enable tqdm for showing progress bar when loading model
     weights."""
+    pt_load_map_location: Union[str, dict[str, str]] = "cpu"
+    """
+    pt_load_map_location: the map location for loading pytorch checkpoint, to
+    support loading checkpoints can only be loaded on certain devices like
+    "cuda", this is equivalent to {"": "cuda"}. Another supported format is
+    mapping from different devices like from GPU 1 to GPU 0:
+    {"cuda:1": "cuda:0"}. Note that when passed from command line, the strings
+    in dictionary needs to be double quoted for json parsing. For more details,
+    see original doc for `map_location` in https://pytorch.org/docs/stable/generated/torch.load.html
+    """
 
     def compute_hash(self) -> str:
         """