tpm2: Introduce TIS tpm core

There's a lot of code duplication in U-Boot right now.  All the TPM TIS
compatible drivers we have at the moment have their own copy of a TIS
implementation.

So let's create a common layer which implements the core TIS functions.
Any driver added from now own, which is compatible with the TIS spec, will
only have to provide the underlying bus communication mechanisms.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>