Move the CUDA implementation of trunc to ATen. (#25423)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25423
Fix #24650
Test Plan: Imported from OSS
Differential Revision: D17397489
Pulled By: VitalyFedyunin
fbshipit-source-id: 933f915a44ff9b7803ddb2708bf0e723433ee0b6
