tpm: Probe for connected TPM 1.2 or TPM 2

In the TPM passthrough backend driver, modify the probing code so
that we can check whether a TPM 1.2 or TPM 2 is being used
and adapt the behavior of the TPM TIS accordingly.

Move the code that tested for a TPM 1.2 into tpm_utils.c
and extend it with test for probing for TPM 2. Have the
function return the version of TPM found.

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>