qemu: tpm: Add support for storing private TPM-related data

qemu: tpm: Add support for storing private TPM-related data

Add support for storing private TPM-related data. The first private data
will be related to the capability of the started swtpm indicating whether
it is capable of migration with a shared storage setup since that requires
support for certain command line flags that were only becoming available
in v0.8.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>