x86/dsputilenc: port sum_abs_dctelem functions to yasm

Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/opusdec: check alignment, misalignment could lead to crashes with avx

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>