tpm: Export the TPM-version functions

These functions should really be available outside the TPM code, so that
other callers can find out which version the TPM is. Rename them to have
a tpm_ prefix() and add them to the header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>