Fix horizontal/horizontal_up 8x8l intra prediction x86/simd functions.
The original functions did not work correctly for edge pixels, e.g.
when CODEC_FLAG_EMU_EDGE is set, leading to corrupt output in e.g. VLC.
Based on a patch by Daniel Kang <daniel d kang gmail com>.

Signed-off-by: Ronald S. Bultje <rsbultje gmail com>
(cherry picked from commit b9c7f66e6da8ac77eaa0c3fb6d476e6fc929b3c9)
