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

Reviewers: efriedma, david-arm, fpetrogalli, arsenm

Reviewed By: david-arm

Subscribers: arsenm, kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, tschuett, hiraditya, rkruppe, psnobl, kerbowa, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D80328