Reason for revert:
Failures on greedy RegAlloc, Fuzzer
Original issue's description:
> Remove register index/code indirection
>
> Previous to this patch, both the lithium and TurboFan register
> allocators tracked allocated registers by "indices", rather than
> the register codes used elsewhere in the runtime. This patch
> ensures that codes are used everywhere, and in the process cleans
> up a bunch of redundant code and adds more structure to how the
> set of allocatable registers is defined.
>
> Some highlights of changes:
>
> * TurboFan's RegisterConfiguration class moved to V8's top level
> so that it can be shared with Crankshaft.
> * Various "ToAllocationIndex" and related methods removed.
> * Code that can be easily shared between Register classes on
> different platforms is now shared.
> * The list of allocatable registers on each platform is declared
> as a list rather than implicitly via the register index <->
> code mapping.
>
> Committed: https://crrev.com/80bc6f6e11f79524e3f1ad05579583adfd5f18b2
> Cr-Commit-Position: refs/heads/master@{#30913}
TBR=akos.palfi@imgtec.com,bmeurer@chromium.org,jarin@chromium.org,paul.lind@imgtec.com,titzer@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
Review URL: https://codereview.chromium.org/1365073002
Cr-Commit-Position: refs/heads/master@{#30914}
3ac27431a9