sysinfo: Don't use fallback when not implemented.

There is no fallback mechanism for BSD systems. We need to avoid
polling here as it will break E on first poll of data.

Essentially, if we fail to find a battery, we use a broken
fallback mechanism which breaks E. Don't do this :)

src/modules/sysinfo/batman/batman_fallback.c

@@ -1251,7 +1251,9 @@ dir_has_contents(const char *dir)
 int
 _batman_fallback_start(Instance *inst)
 {
-#if defined(HAVE_CFBASE_H) /* OS X */
+#if defined(__OpenBSD__) || defined(__DragonFly__) || defined(__FreeBSD__) || defined(__NetBSD__)
+   return 0;
+#elif defined(HAVE_CFBASE_H) /* OS X */
    darwin_init();
 #else
    if ((ecore_file_is_dir(sys_power_dir)) && (dir_has_contents(sys_power_dir)))