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

Reviewers: efriedma, kmclaughlin, sdesmalen, fhahn, bkramer, anna, gchatelet, c-rhodes, david-arm, fpetrogalli

Reviewed By: david-arm

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80336