x86/videodsp: add ff_emu_edge_{hfix,hvar}_avx2

~15% faster than sse2.

Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>
libavutil/opt: fix av_opt_set_channel_layout() to access correct memory address

Signed-off-by: Philip DeCamp <decamp@mit.edu>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>