VP9 common for ARMv8 by using NEON intrinsics 15

Re-write
- vp9_lpf_horizontal_4_dual_neon
in vp9_loopfilter_16_neon.c

Change-Id: Ie14f63d352f9564ad01db3939a61d91cf6d21a31
Signed-off-by: James Yu <james.yu@linaro.org>