KeyedLoadIC should have same register spec as LoadIC.

On arm, arm64 and x64 there is a different register specification between LoadIC and KeyedLoadIC.

It would be nicer if these are the same, allowing some key optimizations.

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/338963003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22103 ce2b1a6d-e550-0410-aec6-3dcde31c8c00