cpuset: Refactor exclusive CPU mask computation logic

cpuset: Refactor exclusive CPU mask computation logic

The current compute_effective_exclusive_cpumask function handles multiple
scenarios with different input parameters, making the code difficult to
follow. This patch refactors it into two separate functions:
compute_excpus and compute_trialcs_excpus.

The compute_excpus function calculates the exclusive CPU mask for a given
input and excludes exclusive CPUs from sibling cpusets when cs's
exclusive_cpus is not explicitly set.

The compute_trialcs_excpus function specifically handles exclusive CPU
computation for trial cpusets used during CPU mask configuration updates,
and always excludes exclusive CPUs from sibling cpusets.

This refactoring significantly improves code readability and clarity,
making it explicit which function to call for each use case and what
parameters should be provided.

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