test_suite_x509write: use plaintext key file

Some test cases are using encrypted key file, thus have
dependency on low-level block cipher modules (e.g. AES).
This commit adds unencrypted key file so that we could
get rid of those dependencies.

Signed-off-by: Pengyu Lv <pengyu.lv@arm.com>
diff --git a/tests/data_files/Makefile b/tests/data_files/Makefile
index 21ca489..51a5d7e 100644
--- a/tests/data_files/Makefile
+++ b/tests/data_files/Makefile
@@ -38,12 +38,15 @@
 
 test_ca_crt = test-ca.crt
 test_ca_key_file_rsa = test-ca.key
+test_ca_key_file_rsa_unenc = test-ca_unenc.key
 test_ca_pwd_rsa = PolarSSLTest
 test_ca_config_file = test-ca.opensslconf
 
 $(test_ca_key_file_rsa):
 	$(OPENSSL) genrsa -aes-128-cbc -passout pass:$(test_ca_pwd_rsa) -out $@ 2048
-all_final += $(test_ca_key_file_rsa)
+$(test_ca_key_file_rsa_unenc): $(test_ca_key_file_rsa)
+	$(OPENSSL) rsa -passin pass:$(test_ca_pwd_rsa) -in $< -out $@
+all_final += $(test_ca_key_file_rsa) $(test_ca_key_file_rsa_unenc)
 
 test-ca.req.sha256: $(test_ca_key_file_rsa)
 	$(MBEDTLS_CERT_REQ) output_file=$@ filename=$(test_ca_key_file_rsa) password=$(test_ca_pwd_rsa) subject_name="C=NL,O=PolarSSL,CN=PolarSSL Test CA" md=SHA256