security: keys: trusted: fix lost handle flush

The original code, before it was moved into security/keys/trusted-keys
had a flush after the blob unseal.  Without that flush, the volatile
handles increase in the TPM until it becomes unusable and the system
either has to be rebooted or the TPM volatile area manually flushed.
Fix by adding back the lost flush, which we now have to export because
of the relocation of the trusted key code may cause the consumer to be
modular.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Fixes: 2e19e101

 ("KEYS: trusted: Move TPM2 trusted keys code")
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>