Small optimizations for conv2d kernel subroutines. (#29188)
Small optimizations for conv2d kernel subroutines. (#29188)

- Make sure that oneDNN memory descriptors are created only once at
first iteration.
PaddlePaddle/Paddle,PaddlePaddle/Paddle,PaddlePaddle/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,luotao1/Paddle,luotao1/Paddle,luotao1/Paddle,luotao1/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,luotao1/Paddle,PaddlePaddle/Paddle,PaddlePaddle/Paddle