Yeah, but the point of having a TPM isn't just to have hardware capable of storing keys and doing some cryptography (so you can e.g. sign a challenge without exposing the private key) but also an hardware that makes extracting the keys from it hard. With an Arduino you can get the first part, but I don't think you can also make it tamper resistant or tamper evident. But still a device that could be interesting to play with, just be aware of the reduced grade of security that you get