[SVE] Eliminate calls to default-false VectorType::get() from X86

Reviewers: efriedma, craig.topper, RKSimon, samparker, kmclaughlin, david-arm

Reviewed By: david-arm

Subscribers: tschuett, hiraditya, rkruppe, psnobl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D81520