Add initial fambench support to e2e_models

[xuzhao9]

Add FAMBench submodule and xlmr support.
The following command runs the fambench xlmr inference:

$ python run_e2e.py fambench_xlmr
{"device": "cuda", "device_num": 1, "test": "eval", "num_examples": 160, "batch_size": 16, "result": {"latency": 23.143840166999997, "qps": 6.913286595719689}}

Adding the FAMBench submodule also enables us to add those models to TorchBench.

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[erichan1]

LGTM! Thanks for adding this to TB!