Add missing compilation guards in test suite

Fix the build when MBEDTLS_USE_PSA_CRYPTO is set but
MBEDTLS_X509_CSR_WRITE_C is not.
diff --git a/tests/suites/test_suite_x509write.function b/tests/suites/test_suite_x509write.function
index 7b369bb..0db2b0e 100644
--- a/tests/suites/test_suite_x509write.function
+++ b/tests/suites/test_suite_x509write.function
@@ -33,7 +33,8 @@
 }
 #endif /* MBEDTLS_RSA_C */
 
-#if defined(MBEDTLS_USE_PSA_CRYPTO)
+#if defined(MBEDTLS_USE_PSA_CRYPTO) && \
+    defined(MBEDTLS_PEM_WRITE_C) && defined(MBEDTLS_X509_CSR_WRITE_C)
 static int x509_crt_verifycsr( const unsigned char *buf, size_t buflen )
 {
     unsigned char hash[MBEDTLS_MD_MAX_SIZE];
@@ -70,7 +71,7 @@
     mbedtls_x509_csr_free( &csr );
     return( ret );
 }
-#endif /* MBEDTLS_USE_PSA_CRYPTO */
+#endif /* MBEDTLS_USE_PSA_CRYPTO && MBEDTLS_PEM_WRITE_C && MBEDTLS_X509_CSR_WRITE_C */
 
 /* END_HEADER */