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

Reviewers: efriedma, david-arm, fpetrogalli, ddunbar, rjmccall

Reviewed By: fpetrogalli, rjmccall

Subscribers: tschuett, rkruppe, psnobl, dmgreen, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D80323