tpm2: change tpm2_unseal() to accept Tpm2Context instead of device string

This matches the change to tpm2_seal(), which now accepts a Tpm2Context instead
of a device string.

This also allows using the same TPM context for sealing and unsealing, which
will be required by (future) test code when sealing/unsealing using a transient
key.

src/cryptenroll/cryptenroll-tpm2.c

@@ -279,7 +279,7 @@ int enroll_tpm2(struct crypt_device *cd,
                 size_t secret2_size;
 
                 log_debug("Unsealing for verification...");
-                r = tpm2_unseal(device,
+                r = tpm2_unseal(tpm2_context,
                                 hash_pcr_mask,
                                 hash_pcr_bank,
                                 pubkey, pubkey_size,