cgroup/cpuset: Skip spread flags update on v2

[ Upstream commit 18f9a4d4 ]

Cpuset v2 has no spread flags to set. So we can skip spread
flags update if cpuset v2 is being used. Also change the name to
cpuset_update_task_spread_flags() to indicate that there are multiple
spread flags.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Stable-dep-of: 42a11bf5 ("cgroup/cpuset: Make cpuset_fork() handle CLONE_INTO_CGROUP properly")
Signed-off-by: Sasha Levin <sashal@kernel.org>