Add updates to LLaMA scripts (#18076)
### Description
This PR adds a few updates to scripts in the LLaMA folder:
- Fixes the precision re-naming in the LLaMA export
- Adds a "prerequisites" section in the README
- Adds IO binding synchronizations during benchmarking for other EPs
### Motivation and Context
- With precision re-naming, the LLaMA parity check does not produce
errors when creating the FP32 CPU model
- The "prerequisites" section shows that there are specific package
versions needed
- This allows for benchmarking with other EPs besides CPU and CUDA
