[WebAssembly][NFC] Reorganize SIMD instructions

Summary:
Reorganize WebAssemblyInstrSIMD.td to put all of the instruction
definitions together, making it easier to see which instructions have
been implemented already. Depends on D51143.

Reviewers: aheejin, dschuff

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

Differential Revision: https://reviews.llvm.org/D51113

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@340504 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed