dm: tpm: Add a 'tpmtest' command

These tests come from Chrome OS code. They are not particularly tidy but can
be useful for checking that the TPM is behaving correctly. Some knowledge of
TPM operation is required to use these.

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