* mv floordiv to phi

* mv elementwise_pow to phi

* fix as review

* move elementwise_div grad

* change mutable_data to alloc

* fix compile bugs

* move elementwise function to funcs directory

* fix compile bugs

* modify according to comment

* remove SetAllocationForOutputTenosr

* add place param for copy kernel

* recover SetAllocationForOutputTenosr

* polish code

* fix empty_dev api bug

* test=allcases

* test=allcases

* fix bug

* recover empty

* recover modify

* rename pten dir to phi

* rename namespace to phi

* rename infrt pten dir to phi

* resolve conflict

* rename pten to phi in cmake

* revert all infrt change

* change needed files

* fix infrt failed

* fix inference failed

[Pten]Refactor elementwise_add grad / double grad / triple grad Kernel and move them to pten (#39048)

* refactor elementwise add grad

* fix compile bugs

* fix unit test bugs

* fix file conflicts

* fix bugs when buildPtenContext