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

Reviewers: efriedma, RKSimon, c-rhodes, fpetrogalli

Reviewed By: fpetrogalli

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D82208