[SVE] Remove calls to VectorType::getNumElements from Transforms/Utils

Reviewers: efriedma, c-rhodes, david-arm, Tyker, asbirlea

Reviewed By: david-arm

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82057