dnxhdenc: make get_pixel_8x4_sym accept ptrdiff_t as stride

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Reviewed-by: "Ronald S. Bultje" <rsbultje@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
x86: convert DNxHDenc inline asm to yasm

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Reviewed-by: "Ronald S. Bultje" <rsbultje@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>