[WebAssembly] Add missing SIMD instruction attributes

Summary:
These attributes are copied from equivalent instructions in
WebAssemblyInstrInfo.td.

Reviewers: aheejin, dschuff

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D51518

llvm-svn: 342104