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

Reviewers: bollu, efriedma, david-arm, fpetrogalli, gchatelet

Reviewed By: fpetrogalli

Subscribers: tschuett, rkruppe, psnobl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80341