This reverts commit f22156bf.

Reason for revert: Lots of compile errors. Try bots sloppy??

Original change's description:
> [Liftoff] Rename kConstant to kI32Const
> 
> This makes it more clear that we only store i32 values as constants in
> the cache state.
> 
> R=​ahaas@chromium.org
> 
> Bug: v8:6600
> Change-Id: I3022e963e864c9c533cbb673bd8502481389799b
> Reviewed-on: https://chromium-review.googlesource.com/853870
> Reviewed-by: Andreas Haas <ahaas@chromium.org>
> Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50437}

TBR=ahaas@chromium.org,clemensh@chromium.org

Change-Id: I6e224d4aa03ff18d6d55e9f8d4726fac711c7665
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:6600
Reviewed-on: https://chromium-review.googlesource.com/857016Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50438}