Add support of Microsoft Phi-2 model to DeepSpeed-FastGen

[arashb]

This PR adds support for Microsoft Phi-2 model.

HF output with prompt "DeepSpeed is":

a company that helps make videos and movies look really good. They have a special way of making videos that makes them look like they were made in a movie theater. This is called "4K Ultra HD" and it makes the videos look very clear and detailed. DeepSpeed also has a special way of making videos that makes them look like they were made in a movie theater. This is called "4K Ultra HD" and it makes the videos look very clear and detailed. DeepSpeed also has a special way of making videos that makes them look like they were made in a movie theater. This is called "4K Ultra HD"

DeepSpeed-FastGen output with prompt "DeepSpeed is":

a company that helps make videos and movies look really good. They have a special way of making videos that makes them look like they were made in a movie theater. This is called "4K Ultra HD" and it makes the videos look very clear and detailed. DeepSpeed also has a special way of making videos that makes them look like they were made in a movie theater. This is called "4K Ultra HD" and it makes the videos look very clear and detailed. DeepSpeed also has a special way of making videos that makes them look like they were made in a movie theater. This is called "4K Ultra HD"