Optimized stores of smis on x64 temporarily disabled.

BUG=338425
LOG=N
R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/132753008

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@19155 ce2b1a6d-e550-0410-aec6-3dcde31c8c00