Reason for revert:
Simulator test failures in RunChangeFloat64ToInt.., RunChangeTaggedToInt32,
div-mul-minus-one

Original issue's description:

> Implement assembler, disassembler tests for all instructions for mips32
> and mips64. Additionally, add missing single precision float instructions
> for r2 and r6 architecture variants in assembler, simulator and disassembler
> with corresponding tests.

BUG=

Review URL: https://codereview.chromium.org/1143473003

Cr-Commit-Position: refs/heads/master@{#28404}