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

Reviewers: efriedma, lhames, sdesmalen, fpetrogalli

Reviewed By: lhames, sdesmalen

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82211