rc: improvements for cbr
asm: avx2 assembly code for idct16x16
denoise_dct asm code: SSE version
denoise_dct: avx2 asm code
copy_cnt_16: avx2 asm code, improved 514.32 cycles -> 313.66 cycles
copy_cnt_32: avx2 asm code, improved 1521.17 cycles -> 934.46 cycles
denoiseDct: align performance data while reporting speedup