AVX2 adaption

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x86_64:
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cdef_filter_4x4_8bpc_c: 1370.2
cdef_filter_4x4_8bpc_ssse3: 142.3
cdef_filter_4x4_8bpc_avx2: 106.7
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cdef_filter_4x8_8bpc_c: 2749.3
cdef_filter_4x8_8bpc_ssse3: 257.2
cdef_filter_4x8_8bpc_avx2: 178.8
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cdef_filter_8x8_8bpc_c: 5609.5
cdef_filter_8x8_8bpc_ssse3: 438.1
cdef_filter_8x8_8bpc_avx2: 250.6
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x86_32:
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cdef_filter_4x4_8bpc_c: 1548.7
cdef_filter_4x4_8bpc_ssse3: 179.8
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cdef_filter_4x8_8bpc_c: 3128.2
cdef_filter_4x8_8bpc_ssse3: 328.1
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cdef_filter_8x8_8bpc_c: 6454.5
cdef_filter_8x8_8bpc_ssse3: 584.4
------------------------------------------