[X86] Don't scalarize v2f32->v2i64 strict_fp_to_sint/uint with avx512dq and not avx512vl.

We can pad the v2f32 with 0s up to v8f32 and use a v8f32->v8i64
operation. This is what we end up with on non-strict nodes except
we don't pad with 0s since we don't care about exceptions.