* rm "paddle/fluid/operators/eigen/eigen_function.h" in phi

* rm "paddle/fluid/operators/elementwise/elementwise_op_function.h" in phi

* Revert "rm "paddle/fluid/operators/elementwise/elementwise_op_function.h" in phi"

This reverts commit c4ba51225e3652f1d80925afba406612968f0ee9.

* move reduce_mean_grad kernel into phi

* move reduce_max/min_grad into phi

* remove raw max/min grad kernel

* fix bug

* fix max/min grad error

* move all reduce_grad kernel into one file

* add prod grad kernel

* add infermeta for prod kernel

* add reduce_sum grad kernel

* add reduce_grad

* modify reduce grad

* update reduce grad functions

* fix build error

* add argument mapping

* move cast input after grad

* add dims.size=1 cpu reduce_sum grad compute method

* update reduce grad GPU

* remove raw reduce_sum_grad kernel

* modify header files

* add namespace funcs for reduce_grad_funcstions