CVE-2017-5754

BugLink: http://bugs.launchpad.net/bugs/1742772

Add a hwsync after DCBT_STOP_ALL_STREAM_IDS to order loads/
stores prior to stopping prefetch with loads and stores
as a part of the flushing. A lwsync is needed to ensure
that after we don't mix the flushing of one congruence class
with another
Signed-off-by: Balbir Singh <bsingharora@gmail.com>
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>