tpm: Add functions to access flags and permissions

Add a few new functions which will be used by the test command in a future
patch.

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>