mb_lpf_horizontal_edge AVX2 optimization

This CL contains two AVX2 optimized loop filter functions,
mb_lpf_horizontal_edge_w_avx2_8 and mb_lpf_horizontal_edge_w_avx2_16.

Change-Id: I604e4fe6e99752b7800c2ea98721d97f7e0b931b
3 files changed