avcodec/x86/lossless_videodsp: use SPLATW in add_int16

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/x86/lossless_videodsp: Port lorens add_hfyu_left_prediction_ssse3/sse4 to 16bit

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/lossless_videodsp: fix diff_int16_c on MIPS

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
fate: add a few tests for >8bpc ffvhuff

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