[X86][AVX] Use lowerShuffleWithPERMV in shuffle combining to support non-VLX targets

lowerShuffleWithPERMV allows us to use the ZMM variants for 128/256-bit variable shuffles on non-VLX AVX512 targets.

This is another step towards shuffle combining through between vector widths - we still end up with an annoying regression (combine_vpermilvar_vperm2f128_zero_8f32) but we're going in the right direction....