Clean up the SSE detection logic. * Include the correct header right in the SSE check in platform.h. * Don't use separate SSE versions of the load functions, have them use SSE automatically. BUG=612205 Change-Id: I70f9a5513e144db4d16c1f3ad922debeb6c50268 Reviewed-on: https://chromium-review.googlesource.com/358108 Reviewed-by: Corentin Wallez <cwallez@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Geoff Lang <geofflang@chromium.org>