[SVE] Remove calls to getBitWidth from mips

Reviewers: efriedma, ahatanak, sdesmalen, c-rhodes, david-arm

Reviewed By: efriedma

Subscribers: dexonsmith, sdardis, arichardson, tschuett, hiraditya, jrtc27, atanasyan, rkruppe, psnobl, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D77906