x86: dsputilenc: move all the function prototypes together

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
x86: dsputilenc: convert ff_sse{8, 16}_mmx() to yasm

Signed-off-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>