cpuset: introduce cpus_excl_conflict and mems_excl_conflict helpers

This patch adds cpus_excl_conflict() and mems_excl_conflict() helper
functions to improve code readability and maintainability. The exclusive
conflict checking follows these rules:

1. If either cpuset has the 'exclusive' flag set, their user_xcpus must
   not have any overlap.
2. If neither cpuset has the 'exclusive' flag set, their
   'cpuset.cpus.exclusive' (only for v2) values must not intersect.
3. The 'cpuset.cpus' of one cpuset must not form a subset of another
   cpuset's 'cpuset.cpus.exclusive'.

Signed-off-by: Chen Ridong <chenridong@huawei.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>