Smi immediates are not supported on x64. Do not use it.

R=jkummerow@chromium.org
BUG=358059
LOG=N

Review URL: https://codereview.chromium.org/217083003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@20409 ce2b1a6d-e550-0410-aec6-3dcde31c8c00