* move elementwise_div grad

* change mutable_data to alloc

* fix compile bugs

* 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

* transfer: string tinyformat errors and part of enforce into pten

* remove comment

* fix by code review

* assert is not compile in -DNDEBUG

* add string as dependences of paddle_inference

* Migrate Dim and DDim from paddle::framework into pten namespace

* fix paddle::framework::Array

* fix framework::Array

* Migrate bfloat16/float16/complex from platform into pten::common

* fix typo

* fix code style

* change 'math' to 'math_kernel'

* fix compile bugs

* merge develop

* fix compile bugs

* move cpu_impl of elementwise kernel to new directory