[turbofan] Use load/store indexes as 64-bit registers on arm64.

Since r25024 load/store indexes are 64-bit value but arm64 backend was still
treating them as 32-bit value.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/698383003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25144 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Revert "Reland "Optimize function across closures.""

This reverts commit r25142.

TBR=ishell@chromium.org

Review URL: https://codereview.chromium.org/702853002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@25145 ce2b1a6d-e550-0410-aec6-3dcde31c8c00