add BFloat16 to aten_bridge (pytorch#5519)

Summary:
Pull Request resolved: pytorch#5519

Discovered these were missing while trying to use the following diff.
ghstack-source-id: 243867517
exported-using-ghexport

Reviewed By: digantdesai

Differential Revision: D63147276

fbshipit-source-id: bf75fb0fe452e2e68a34271ca1250cdb90657e5a

Author: swolchok

extension/aten_util/aten_bridge.cpp

@@ -73,6 +73,8 @@ torch::executor::ScalarType torch_to_executorch_scalar_type(
       return torch::executor::ScalarType::Short;
     case c10::ScalarType::Half:
       return torch::executor::ScalarType::Half;
+    case c10::ScalarType::BFloat16:
+      return torch::executor::ScalarType::BFloat16;
     case c10::ScalarType::Int:
       return torch::executor::ScalarType::Int;
     case c10::ScalarType::Float:
@@ -103,6 +105,8 @@ c10::ScalarType executorch_to_torch_scalar_type(
       return c10::ScalarType::Short;
     case torch::executor::ScalarType::Half:
       return c10::ScalarType::Half;
+    case torch::executor::ScalarType::BFloat16:
+      return c10::ScalarType::BFloat16;
     case torch::executor::ScalarType::Int:
       return c10::ScalarType::Int;
     case torch::executor::ScalarType::Float: