ARM: Merge redundant entries in literal pool.

This patch also clean up 64-bits literals handling.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/61763025

Patch from Rodolph Perfetta <rodolph.perfetta@gmail.com>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@17789 ce2b1a6d-e550-0410-aec6-3dcde31c8c00