[WebAssembly] Add V128 value type to binary format

Summary: Adds the necessary support to lib/ObjectYAML and fixes SIMD
calls to allow the tests to work. Also removes some dead code that
would otherwise have to have been updated.

Reviewers: aheejin, dschuff, sbc100

Subscribers: jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D52105

llvm-svn: 342689