i965: Enable flush control
Reviewed-by:Adam Jackson <ajax@redhat.com> Reviewed-by:
Nicolai Hähnle <nicolai.haehnle@amd.com> Reviewed-by:
Emil Velikov <emil.velikov@collabora.com> Reviewed-by:
Kenneth Graunke <kenneth@whitecape.org> Signed-off-by:
Neil Roberts <neil@linux.intel.com>