dm: tpm: Add Driver Model support for tpm_atmel_twi driver

tpm_atmel_twi can fit perfectly to the new UCLASS_TPM class.

Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Acked-by: Simon Glass <sjg@chromium.org>