tls: replace ECDH_C guards with new helpers

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
diff --git a/library/ssl_client.c b/library/ssl_client.c
index 9acc44f..dc2b650 100644
--- a/library/ssl_client.c
+++ b/library/ssl_client.c
@@ -374,7 +374,8 @@
         }
 
 #if defined(MBEDTLS_SSL_PROTO_TLS1_2) && \
-        (defined(MBEDTLS_ECDH_C) || defined(MBEDTLS_ECDSA_C) || \
+        (defined(MBEDTLS_KEY_EXCHANGE_SOME_ECDH_OR_ECDHE_1_2_ENABLED) || \
+        defined(MBEDTLS_ECDSA_C) || \
         defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED))
         *tls12_uses_ec |= mbedtls_ssl_ciphersuite_uses_ec(ciphersuite_info);
 #endif