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

Reviewers: efriedma, aymanmus, c-rhodes, david-arm

Reviewed By: david-arm

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80332