Support compute_uinit in coreml backend when calling ct.convert (#4059)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/4059

It seems currently the compute unit value set in https://www.internalfb.com/code/fbsource/fbcode/executorch/examples/models/llama2/lib/partitioner_lib.py?lines=74 is not used during the convert, adding the support in this diff.

However to my surprise, the model name in the actual ios instrument result has the right suffix (see the image below), I couldn't find anywhere in the code how this is set and I have no way to validate if it's just part of the name or it's indeed set correctly through another path. I'll abandon this diff if it's not needed actually...

 {F1718372833}

Reviewed By: cccclai

Differential Revision: D58981934

fbshipit-source-id: e0b5db07547abe270ae7c8fbd87547428afe93af