tracing: rename EVENT_TRACER config to ENABLE_EVENT_TRACING

Currently we have two configs: EVENT_TRACING and EVENT_TRACER.
All tracers enable EVENT_TRACING. The EVENT_TRACER is only a
convenience to enable the EVENT_TRACING when no other tracers
are enabled.

The names EVENT_TRACER and EVENT_TRACING are too similar and confusing.
This patch renames EVENT_TRACER to ENABLE_EVENT_TRACING to be more
appropriate to what it actually does, as well as add a comment in
the help menu to explain the option's purpose.

[ Impact: rename config option to reduce confusion ]
Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/Kconfig

@@ -183,7 +183,7 @@ config CONTEXT_SWITCH_TRACER
 	  This tracer gets called from the context switch and records
 	  all switching of tasks.
 
-config EVENT_TRACER
+config ENABLE_EVENT_TRACING
 	bool "Trace various events in the kernel"
 	select TRACING
 	help
@@ -191,6 +191,10 @@ config EVENT_TRACER
 	  allowing the user to pick and choose which trace point they
 	  want to trace.
 
+	  Note, all tracers enable event tracing. This option is
+	  only a convenience to enable event tracing when no other
+	  tracers are selected.
+
 config FTRACE_SYSCALLS
 	bool "Trace syscalls"
 	depends on HAVE_FTRACE_SYSCALLS