[X86][AVX] createVariablePermute - use 2xVPERMIL+PCMPGT+SELECT for v8i32/v8f32...

[X86][AVX] createVariablePermute - use 2xVPERMIL+PCMPGT+SELECT for v8i32/v8f32 and v4i64/v4f64 variable permutes

As VPERMILPS/VPERMILPD only selects elements based on the bits[1:0]/bit[1] then we can permute both the (repeated) lo/hi 128-bit vectors in each case and then select between these results based on whether the index was for for lo/hi.

For v4i64/v4f64 this avoids some rather nasty v4i64 multiples on the AVX2 implementation, which seems to be worse than the extra port5 pressure from the additional shuffles/blends.

llvm-svn: 327239