x86: add AVX2 SIMD for ipred.cfl_ac[444]
cfl_ac_444_w4_8bpc_c: 499.1
cfl_ac_444_w4_8bpc_ssse3: 24.3
cfl_ac_444_w4_8bpc_avx2: 28.9
cfl_ac_444_w8_8bpc_c: 1240.2
cfl_ac_444_w8_8bpc_ssse3: 47.4
cfl_ac_444_w8_8bpc_avx2: 34.9
cfl_ac_444_w16_8bpc_c: 1785.7
cfl_ac_444_w16_8bpc_ssse3: 86.7
cfl_ac_444_w16_8bpc_avx2: 54.6
cfl_ac_444_w32_8bpc_c: 4343.5
cfl_ac_444_w32_8bpc_ssse3: 236.5
cfl_ac_444_w32_8bpc_avx2: 113.6