[SVE] Remove calls to VectorType::getNumElements from mlir

Reviewers: efriedma, ftynse, rriddle

Reviewed By: ftynse, rriddle

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

Tags: #mlir

Differential Revision: https://reviews.llvm.org/D82583