Support authentication of uefi priv. variables

To authenticate private uefi variables a fingerprint has to be
calculated based on the common name of the signing certificate's
Subject field and the tbsCertificate of the top-level issuer
certificate.
These variables have a public key certificate attached so the
verify_pkcs7_signature_handler is also reorganized to be able
to verify its own signature with its internal public key.
This commit implements the changes needed for the described
functionality.

Signed-off-by: Gabor Toth <gabor.toth2@arm.com>
Change-Id: Ida22977f3ef1a730ea95834ca5c9f9e4ed78d927
diff --git a/components/service/crypto/client/psa/crypto_client.h b/components/service/crypto/client/psa/crypto_client.h
index 4b59bbe..af04df1 100644
--- a/components/service/crypto/client/psa/crypto_client.h
+++ b/components/service/crypto/client/psa/crypto_client.h
@@ -7,10 +7,15 @@
 #ifndef CRYPTO_CLIENT_H
 #define CRYPTO_CLIENT_H
 
+#include <stddef.h>
 #include <stdint.h>
 
 int verify_pkcs7_signature(const uint8_t *signature_cert, uint64_t signature_cert_len,
 			   const uint8_t *hash, uint64_t hash_len, const uint8_t *public_key_cert,
 			   uint64_t public_key_cert_len);
 
+int get_uefi_priv_auth_var_fingerprint_handler(const uint8_t *signature_cert,
+				    uint64_t signature_cert_len,
+				    uint8_t *output);
+
 #endif /* CRYPTO_CLIENT_H */