tests: ztest: add system logging header file

This patch eliminates need to add logging/sys_log.h in test
cases which required to use this header file.

Signed-off-by: Punit Vara <punit.vara@intel.com>
diff --git a/tests/ztest/include/ztest.h b/tests/ztest/include/ztest.h
index e21032f..be6cd69 100644
--- a/tests/ztest/include/ztest.h
+++ b/tests/ztest/include/ztest.h
@@ -47,5 +47,6 @@
 #include <ztest_mock.h>
 #include <ztest_test.h>
 #include <tc_util.h>
+#include <logging/sys_log.h>
 
 #endif /* __ZTEST_H__ */