tpm: update descriptions in tpm headers

tpm: update descriptions in tpm headers

* Provide a link to 'TPM 2.0 Library Specification'
* Remove outdated comment for TPM2_NUM_PCR_BANKS.
  The value 16 can be found in the current standard
  TCG TSS 2.0 Overview and Common Structures Specification 1.0, rev 10
* Describe some of the structures in Sphinx style.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>