tpm_emulator: Avoid double initialization during migration

tpm_emulator: Avoid double initialization during migration

When resuming after a migration, the backend sends CMD_INIT to the
emulator from the startup callback, then it sends the migration state
from the vmstate to the emulator, then it sends CMD_INIT again. Skip the
first CMD_INIT during a migration to avoid initializing the TPM twice.

Signed-off-by: Ross Lagerwall <ross.lagerwall@citrix.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Tested-by: Stefan Berger <stefanb@linux.ibm.com>
Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>