x64: Implement DoArgumentsElements, DoNumberUntagD, DoArgumentsLength,
DoAccessArgumentsAt, DoStringLength in lithium x64 backend.

Fix a bug in DoConstantD where only 32-bits of a double was loaded to
an xmm register.

Review URL: http://codereview.chromium.org/6474039

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@6771 ce2b1a6d-e550-0410-aec6-3dcde31c8c00