cgroup: Merge branch 'for-4.3-fixes' into for-4.4

Pull to receive 9badce00 ("cgroup, writeback: don't enable cgroup
writeback on traditional hierarchies").  The commit adds
cgroup_on_dfl() usages in include/linux/backing-dev.h thus causing a
silent conflict with 9e10a130 ("cgroup: replace cgroup_on_dfl()
tests in controllers with cgroup_subsys_on_dfl()").  The conflict is
fixed during this merge.

Signed-off-by: Tejun Heo <tj@kernel.org>