Rounding mode should be round-to-nearest by default, and NaN mode bit
should be 0, like in a real ARM system.

BUG=3253
LOG=N
R=rmcilroy@chromium.org

Review URL: https://codereview.chromium.org/235893005

Patch from Olli Etuaho <oetuaho@nvidia.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20725 ce2b1a6d-e550-0410-aec6-3dcde31c8c00