[quant] Add support for symmetric quant in executorch (#90304)
Summary:
This PR adds symmetric quant in the backend config for executorch
Test Plan:
NA, will be tested in meta internal flow
Reviewers:
Subscribers:
Tasks:
Tags:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90304
Approved by: https://github.com/cccclai, https://github.com/jcaip, https://github.com/andrewor14
