rust/pv: Add decrypt and HMAC function

Add a function to decrypt a block with aes_gcm.
Add functionality to perform HMAC operations.

Acked-by: Qi Feng Huo <huoqif@cn.ibm.com>
Acked-by: Marc Hartmayer <mhartmay@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>

rust/pv/src/error.rs

@@ -50,6 +50,9 @@ pub enum Error {
     #[error("Customer Communication Key must be 32 bytes long")]
     CckSize,
 
+    #[error("Decryption failed. Probably due to a GCM tag mismatch.")]
+    GcmTagMismatch,
+
     #[error("Invalid {0} user-data for signing provided. Max {} bytes allowed", .0.max())]
     AsrcbInvSgnUserData(UserDataType),