[fx] update split module pass and add customized policy

[YuliangLiu0306]

This PR mainly do two things:

1. Update split module pass: In past split module pass, it treats partitions as a DAG, but we need treat them as a single direction linked list in pipeline parallel. The difference is if a output from partition 0 is an input argument of partition 3, the DAG will not transfer it to partition 1 and partition 2. However, in single direction linked list, we need to do so.
2. Add customized split policy: The customized policy will make the performance test easier for us.