[BE] use DeviceIndex instead of int64_t for related device interfaces (#103068)

This PR unifies the device interfaces in aten/*cpp and torch/csrc/*cpp to use  **c10::DeviceIndex**.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/103068
Approved by: https://github.com/malfet

torchgen/model.py

@@ -1803,6 +1803,7 @@ class BaseTy(Enum):
     bool = auto()
     Layout = auto()
     Device = auto()
+    DeviceIndex = auto()
     Scalar = auto()
     MemoryFormat = auto()
     QScheme = auto()