[WebAssembly] Expand more SIMD float ops

Summary: These were previously causing ISel failures.

Reviewers: aheejin

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62354

llvm-svn: 361577