tpm/tpm_i2c_stm_st33/dts/st33zp24_i2c: Add DTS Documentation

st33zp24 tpm can be seen as a trivial i2c device as other i2c tpm.
However several other properties needs to be documented such as lpcpd.

Reviewed-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Signed-off-by: Christophe Ricard <christophe-h.ricard@st.com>
Signed-off-by: Peter Huewe <peterhuewe@gmx.de>