library: replace deprecated symbols with temporary _LEGACY ones

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/include/mbedtls/psa_util.h b/include/mbedtls/psa_util.h
index 528c0ab..1418b85 100644
--- a/include/mbedtls/psa_util.h
+++ b/include/mbedtls/psa_util.h
@@ -341,7 +341,7 @@
 #endif
 
 #if defined(PSA_WANT_KEY_TYPE_RSA_PUBLIC_KEY) ||    \
-    defined(PSA_WANT_KEY_TYPE_RSA_KEY_PAIR)
+    defined(MBEDTLS_PSA_WANT_KEY_TYPE_RSA_KEY_PAIR_LEGACY)
 extern const mbedtls_error_pair_t psa_to_pk_rsa_errors[8];
 #endif