Method half impl_sqrt

tensorflow/core/kernels/training_ops_gpu.cu.cc:52–54

}
template <>
__device__ Eigen::half impl_sqrt(Eigen::half x) {
  return __float2half(sqrt(__half2float(x)));
}
template <>
__device__ Eigen::half impl_rsqrt(Eigen::half x) {
  return __float2half(rsqrt(__half2float(x)));