tpm2: Add a TPMv2 MMIO TIS driver

Add support for devices that expose a TPMv2 though MMIO.
Apart from those devices, we can use the driver in our QEMU setups and
test TPM related code which is difficult to achieve using the sandbox
driver (e.g test the EFI TCG2 protocol).

It's worth noting that a previous patch added TPMv2 TIS core functions,
which the current driver is consuming.

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