The width 16 epel functions never use four taps in any direction*,
so don't build said functions. Saves 4352B of .text and 89B of
.text.unlikely here.
*: mx and my in vp8_mc_luma() are always even.
Reviewed-by: Ronald S. Bultje <rsbultje@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>