ARM64: avoid duplicate load of double constants

R=bmeurer@chromium.org, ulan@chromium.org

BUG=

Review URL: https://codereview.chromium.org/357973002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22051 ce2b1a6d-e550-0410-aec6-3dcde31c8c00