Add rules to generate server4.crt

Signed-off-by: Pengyu Lv <pengyu.lv@arm.com>
diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index 94aace6..c066e05 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -1182,6 +1182,12 @@
 	$(MBEDTLS_CERT_WRITE) subject_key=$< subject_name="C=NL,O=PolarSSL,CN=localhost" serial=13 issuer_crt=$(test_ca_crt) issuer_key=$(test_ca_key_file_rsa) issuer_pwd=$(test_ca_pwd_rsa) not_before=20190210144406 not_after=20290210144406 md=SHA1 version=3 output_file=$@
 all_final += server3.crt
 
+# server4*
+
+server4.crt: server4.key
+	$(MBEDTLS_CERT_WRITE) subject_key=$< subject_name="C=NL,O=PolarSSL,CN=localhost" serial=8 issuer_crt=$(test_ca_crt_file_ec) issuer_key=$(test_ca_key_file_ec) not_before=20190210144400 not_after=20290210144400 md=SHA256 version=3 output_file=$@
+all_final += server4.crt
+
 # MD2, MD4, MD5 test certificates
 
 cert_md_test_key = $(cli_crt_key_file_rsa)