log: Disable the syslog driver by default

This driver interferes with other sandbox tests since it causes log output
to be interspersed with "No ethernet found." messages. Disable this driver
by default.

Enable it for the syslog tests so that they still pass.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/test/log/syslog_test.h b/test/log/syslog_test.h
index 75900f3..1310257 100644
--- a/test/log/syslog_test.h
+++ b/test/log/syslog_test.h
@@ -47,4 +47,20 @@
  */
 int sb_log_tx_handler(struct udevice *dev, void *packet, unsigned int len);
 
+/**
+ * syslog_test_setup() - Enable syslog logging ready for tests
+ *
+ * @uts: Test state
+ * @return 0 if OK, -ENOENT if the syslog log driver is not found
+ */
+int syslog_test_setup(struct unit_test_state *uts);
+
+/**
+ * syslog_test_finish() - Disable syslog logging after tests
+ *
+ * @uts: Test state
+ * @return 0 if OK, -ENOENT if the syslog log driver is not found
+ */
+int syslog_test_finish(struct unit_test_state *uts);
+
 #endif