tracing: Add LATENCY_FS_NOTIFY to define if latency_fsnotify() is defined

With the coming addition of the osnoise tracer, the configs needed to
include the latency_fsnotify() has become more complex, and to keep the
declaration in the header file the same as in the C file, just have the
logic needed to define it in one place, and that defines LATENCY_FS_NOTIFY
which will be used in the C code.

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>