selftests: ftrace: Make func_event_triggers and func_traceonoff_triggers tests do instances

Both the func_event_triggers and func_traceonoff_triggers tests can be
performed in both the toplevel instance as well as for individual instances.
Have their tests run in both cases.
Acked-by: NMasami Hiramatsu <mhiramat@kernel.org>
Acked-by: NNamhyung Kim <namhyung@kernel.org>
Signed-off-by: NSteven Rostedt (VMware) <rostedt@goodmis.org>

tools/testing/selftests/ftrace/test.d/ftrace/func_event_triggers.tc

 #!/bin/sh
 # description: ftrace - test for function event triggers
+# flags: instance
 #
 # Ftrace allows to add triggers to functions, such as enabling or disabling
 # tracing, enabling or disabling trace events, or recording a stack trace

tools/testing/selftests/ftrace/test.d/ftrace/func_traceonoff_triggers.tc

 #!/bin/sh
 # description: ftrace - test for function traceon/off triggers
+# flags: instance
 #
 # Ftrace allows to add triggers to functions, such as enabling or disabling
 # tracing, enabling or disabling trace events, or recording a stack trace