[WebAssembly] Update SIMD binary arithmetic

Add missing SIMD types (v2f64) and binary ops. Also adds
tablegen support for automatically prepending prefix byte to SIMD
opcodes.

Differential Revision: https://reviews.llvm.org/D50292

Patch by Thomas Lively

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@339186 91177308-0d34-0410-b5e6-96231b3b80d8
15 files changed