[nrf noup] bootutil: Add error log on KMU not provisioned

An unprovisioned KMU can cause confusion, so improve the logs for this
case.

Signed-off-by: Sigurd Hellesvik <[email protected]>

Author: hellesvik-nordic

boot/bootutil/src/ed25519_psa.c

@@ -126,6 +126,9 @@ int ED25519_verify(const uint8_t *message, size_t message_len,
         }
 
         BOOT_LOG_ERR("ED25519 signature verification failed %d", status);
+        if(status == PSA_ERROR_INVALID_HANDLE) {
+          BOOT_LOG_ERR("PSA_ERROR_INVALID_HANDLE(-136) could mean that the KMU slot is not provisioned.");
+        }
     }
 
     return ret;