dm: tpm: sandbox: Convert TPM driver to driver model

Convert the sandbox TPM driver to use driver model. Add it to the device
tree so that it can be found on start-up.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Christophe Ricard <christophe-h.ricard@st.com>
Reviewed-by: Heiko Schocher <hs@denx.de>