Align names to use "opaque" only everywhere

It's better for names in the API to describe the "what" (opaque keys) rather
than the "how" (using PSA), at least since we don't intend to have multiple
function doing the same "what" in different ways in the foreseeable future.
diff --git a/include/mbedtls/pk_internal.h b/include/mbedtls/pk_internal.h
index 7288e9b..fc9ba13 100644
--- a/include/mbedtls/pk_internal.h
+++ b/include/mbedtls/pk_internal.h
@@ -136,7 +136,7 @@
 #endif
 
 #if defined(MBEDTLS_USE_PSA_CRYPTO)
-extern const mbedtls_pk_info_t mbedtls_pk_opaque_psa_info;
+extern const mbedtls_pk_info_t mbedtls_pk_opaque_info;
 #endif
 
 #endif /* MBEDTLS_PK_WRAP_H */