[mlir] [VectorOps] Rename Utils.h into VectorUtils.h

Summary:
First step towards the consolidation
of a lot of vector related utilities
that are now all over the place
(or even duplicated).

Reviewers: nicolasvasilache, andydavis1

Reviewed By: nicolasvasilache, andydavis1

Subscribers: merge_guards_bot, mehdi_amini, rriddle, jpienaar, burmako, shauheen, antiagainst, arpith-jacob, mgester, lucyrfox, liufengdb, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D72955