TPM2 ACPI table support

Add a TPM2 ACPI table if a TPM 2 is used in the backend.
Also add an SSDT for the TPM 2.

Rename tpm_find() to tpm_get_version() and have this function
return the version of the TPM found, TPMVersion_Unspec if
no TPM is found. Use the version number to build version
specific ACPI tables.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>