[Dynamo] modify IPEX backend (#92067)
1. Combine the two backends ‘ipex_fp32’ and ‘ipex_bf16’ into one backend ‘ipex’.
2. Modify IPEX backend to work in fake mode and symbolic mode.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/92067
Approved by: https://github.com/jgong5, https://github.com/jansel
