rust: Add EBC support to pv_core library

Add EBC (Early Boot Customization) utility functions to pv_core library
for parsing and verifying Add-Secret-Request structures.

Introduce the core library functionality needed for EBC:
- Add ebc_utils module to pv_core with ASR parsing and verification
- Export ebc_utils in pv_core lib.rs
- Re-export ebc_utils in pv lib.rs for downstream consumers
- Update pvsecret Cargo.toml dependencies

The library provides the foundation for tools that work with
integrity-protected ASR structures used in SEL guest customization.

Assisted-by: IBM Bob:1.0.1
Acked-by: Holger Dengler <dengler@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Signed-off-by: Finn Callies <fcallies@linux.ibm.com>
Signed-off-by: Jan Höppner <hoeppner@linux.ibm.com>

rust/pv/src/lib.rs

@@ -104,7 +104,14 @@ pub mod request {
 
     /// Reexports some useful OpenSSL symbols
     pub mod openssl {
-        pub use openssl::{error::ErrorStack, hash::DigestBytes, nid::Nid, pkey, x509};
+        pub use openssl::{
+            error::ErrorStack,
+            hash::DigestBytes,
+            nid::Nid,
+            pkey,
+            sha::{Sha256, Sha512},
+            x509,
+        };
         // rust-OpenSSL does not define these NIDs
         #[allow(missing_docs)]
         pub const NID_ED25519: Nid = Nid::from_raw(openssl_sys::NID_ED25519);
@@ -113,6 +120,8 @@ pub mod request {
     }
 
     pub use pv_core::request::*;
+
+    pub use pv_core::PolicyReference;
 }
 
 /// Functionalities for creating add-secret requests