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

Reviewers: efriedma, ftynse, c-rhodes, david-arm, rriddle

Reviewed By: ftynse

Subscribers: tschuett, rkruppe, psnobl, mehdi_amini, rriddle, jpienaar, shauheen, antiagainst, nicolasvasilache, arpith-jacob, mgester, lucyrfox, liufengdb, stephenneuendorffer, Joonsoo, grosul1, frgossen, Kayjukh, jurahul, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80340