tracing/boot: Add per-event settings

Add per-event settings for boottime tracing. User can set filter,
actions and enable on each event on boot. The event entries are
under ftrace.event.GROUP.EVENT node (note that the option key
includes event's group name and event name.) This supports below
configs.

 - ftrace.event.GROUP.EVENT.enable
   Enables GROUP:EVENT tracing.

 - ftrace.event.GROUP.EVENT.filter = FILTER
   Set FILTER rule to the GROUP:EVENT.

 - ftrace.event.GROUP.EVENT.actions = ACTION[, ACTION2...]
   Set ACTIONs to the GROUP:EVENT.

For example,

  ftrace.event.sched.sched_process_exec {
                filter = "pid < 128"
		enable
  }

this will enable tracing "sched:sched_process_exec" event
with "pid < 128" filter.

Link: http://lkml.kernel.org/r/157867238942.17873.11177628789184546198.stgit@devnote2

Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace_events_trigger.c

@@ -213,7 +213,7 @@ static int event_trigger_regex_open(struct inode *inode, struct file *file)
 	return ret;
 }
 
-static int trigger_process_regex(struct trace_event_file *file, char *buff)
+int trigger_process_regex(struct trace_event_file *file, char *buff)
 {
 	char *command, *next = buff;
 	struct event_command *p;