MIPS: KeyedLoadIC should have same register spec as LoadIC.

Port r22103 (2c36867)

Original commit message:
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.

BUG=
R=palfia@homejinni.com

Review URL: https://codereview.chromium.org/367053002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22168 ce2b1a6d-e550-0410-aec6-3dcde31c8c00
Harden Runtime_LiveEditCheckAndDropActivations against unsafe args.

R=jarin@chromium.org
BUG=390925
LOG=N

Review URL: https://codereview.chromium.org/362983004

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22169 ce2b1a6d-e550-0410-aec6-3dcde31c8c00