tpm: Support for TIS selftest done flag

Extend the backend to check whether the TPM_ContinueSelfTest
finished successfully and provide a flag to the TIS front-end
if it successfully finished. The TIS then sets a flag in
all localities in the STS register and keeps it until the next
reset.

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