adding some better optimized code pieces
adding some better optimized code pieces

tingxingdong/rocFFT-1,ROCmSoftwarePlatform/rocFFT,tingxingdong/rocFFT-1,tingxingdong/rocFFT-1,bragadeesh/rocFFT,ROCmSoftwarePlatform/rocFFT,bragadeesh/rocFFT,ROCmSoftwarePlatform/rocFFT,bragadeesh/rocFFT,ROCmSoftwarePlatform/rocFFT