tpm: Allow disabling platform hierarchy with TPM2

With TPM2 we don't actually lock the TPM once verified boot is finished.
Instead we disable the platform hierarchy which serves the same purpose.
Add an implementation of this so we can safely boot into the kernel.

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