[AMDGPU] Strengthen export cluster ordering

Summary:
When removing barrier edges on exports then dependencies need to
be propagated.

Reviewers: foad

Reviewed By: foad

Subscribers: arsenm, kzhuravl, jvesely, wdng, nhaehnle, yaxunl, dstuttard, tpr, t-tye, hiraditya, kerbowa, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D79855