What does this PR do?

Add dbrx to transformers from https://github.com/databricks/dbrx/tree/main/model.

To run dbrx:

from transformers import DbrxForCausalLM
model = DbrxForCausalLM.from_pretrained(
    "databricks/dbrx-instruct",
    device_map="auto",
    )

Fixes # (issue)

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