[turbofan]: Fix TurboFan for out-of-line constant pool on Arm.

Use LeaveFrame so that the constant pool pointer register is correctly restored
when using the out-of-line constant pool.  Also clean up duplicate code in
builtins-arm.cc.

R=bmeurer@chromium.org

Review URL: https://codereview.chromium.org/469283002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@23134 ce2b1a6d-e550-0410-aec6-3dcde31c8c00