This is reland of 3e0bf580
Original change's description:
> This commit is a step toward enabling test-run-wasm-simd tests for MIPS.
> 36 of those were failing in V8 builtin simulator because some instructions
> were not implemented.  Also there are minor fixes to some of the already
> implemented instructions.
>
> This commit has only 32-bit implementation. After review I will add
> 64-bit version.
>
> Bug:
> Change-Id: I25b0cac352db3efb56b922ace64ab2aaef82472d
> Reviewed-on: https://chromium-review.googlesource.com/744008
> Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
> Cr-Commit-Position: refs/heads/master@{#49439}

Bug: 
Change-Id: I3a904caf675d314186c02c1c843d1e6a91a21a14
Reviewed-on: https://chromium-review.googlesource.com/776813Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#49666}