* add prim erf grad

* add yaml config for prim erf grad

* add math.h

* add cmath

* add math  defines

* use define math

* use define math

* define M_2_SQRTPI

* M_2_SQRTPI math

* try math.h

* fix typro

* remove pow in erf grad

* use new optest

* add fp16 fp32 test

* remove fp16 test