[bssl] Support EC P-384 key in libbssl_avf_nostd

The support of EC P-384 key is required for the verification the
signatures of DiceChainEntry in the service VM.

Test: atest libbssl_avf_nostd.test
Change-Id: I1817a913c6b9be96eed4bc2c86d032f24441386c
diff --git a/libs/bssl/tests/eckey_test.rs b/libs/bssl/tests/eckey_test.rs
index 968af63..2eb908a 100644
--- a/libs/bssl/tests/eckey_test.rs
+++ b/libs/bssl/tests/eckey_test.rs
@@ -57,8 +57,18 @@
 }
 
 #[test]
-fn cose_public_key_serialization() -> Result<()> {
+fn p256_cose_public_key_serialization() -> Result<()> {
     let mut ec_key = EcKey::new_p256()?;
+    check_cose_public_key_serialization(&mut ec_key)
+}
+
+#[test]
+fn p384_cose_public_key_serialization() -> Result<()> {
+    let mut ec_key = EcKey::new_p384()?;
+    check_cose_public_key_serialization(&mut ec_key)
+}
+
+fn check_cose_public_key_serialization(ec_key: &mut EcKey) -> Result<()> {
     ec_key.generate_key()?;
     let cose_key = ec_key.cose_public_key()?;
     let cose_key_data = cose_key.clone().to_vec().unwrap();