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

Reviewers: efriedma, c-rhodes, david-arm, spatel, craig.topper, aqjune, paquette, arsenm, gchatelet

Reviewed By: spatel, gchatelet

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80313