Introduce device type and utility functions

Summary: Introduce device type and utility functions in common types module

Reviewed By: nikhilaravi

Differential Revision: D28970930

fbshipit-source-id: 191ec07390ed66a958c23eb2b43229312492e0b7

pytorch3d/common/types.py

+# Copyright (c) Facebook, Inc. and its affiliates. All rights reserved.
+
+from typing import Optional, Union
+
+import torch
+
+
+Device = Union[str, torch.device]
+
+
+def make_device(device: Device) -> torch.device:
+    return torch.device(device) if isinstance(device, str) else device
+
+
+def get_device(x, device: Optional[Device] = None) -> torch.device:
+    # User overrides device
+    if device is not None:
+        return make_device(device)
+
+    # Set device based on input tensor
+    if torch.is_tensor(x):
+        return x.device
+
+    # Default device is cpu
+    return torch.device("cpu")