[llvm] [HEXAGON] [MachinePipeliner] Fix the DAG in case of dependent phis. (PR #135925)

[Ryotaro Kasuga via llvm-commits]

https://github.com/kasuga-fj commented:

Can you please update the PR description? Not only a single concrete case, more descriptive message, like "add a PHI-PHI dependency properly when...".

It also contains "Authored by: Sumanth Gundapaneni", which does't seem to your name? Is it okay?

https://github.com/llvm/llvm-project/pull/135925