VP8 encoder for ARMv8 by using NEON intrinsics 3

Add subtract_neon.c
- vp8_subtract_b_neon
- vp8_subtract_mby_neon
- vp8_subtract_mbuv_neon

Change-Id: If9a17a093478552e3e3276eeaa3f098b9021d08c
Signed-off-by: James Yu <james.yu@linaro.org>
5 files changed