tpm2: support policies with PIN

Modify TPM2 authentication policy to optionally include an authValue, i.e.
a password/PIN. We use the "PIN" terminology since it's used by other
systems such as Windows, even though the PIN is not necessarily numeric.

The pin is hashed via SHA256 to allow for arbitrary length PINs.

v2: fix tpm2_seal in sd-repart
v3: applied review feedback

src/partition/repart.c

@@ -2656,7 +2656,7 @@ static int partition_encrypt(
                 uint16_t pcr_bank, primary_alg;
                 int keyslot;
 
-                r = tpm2_seal(arg_tpm2_device, arg_tpm2_pcr_mask, &secret, &secret_size, &blob, &blob_size, &hash, &hash_size, &pcr_bank, &primary_alg);
+                r = tpm2_seal(arg_tpm2_device, arg_tpm2_pcr_mask, NULL, &secret, &secret_size, &blob, &blob_size, &hash, &hash_size, &pcr_bank, &primary_alg);
                 if (r < 0)
                         return log_error_errno(r, "Failed to seal to TPM2: %m");