Fix CUDA memory management issues caused by not using PinnedCPUAllocator (#38066)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38066
Increasing priority for PinnedCPUAllocator to make sure it is set when CUDA is enabled.
Test Plan: buck test mode/dev-nosan //vision/fair/detectron2/tests:test_export_caffe2 -- 'testMaskRCNNGPU \(test_export_caffe2\.TestCaffe2Export\)'
Reviewed By: ppwwyyxx
Differential Revision: D21465835
fbshipit-source-id: 643cff30d35c174085e5fde5197ddb05885b2e99
