ftrace: document function and function graph implementation

While implementing function tracer and function tracer graph support,
I found the exact arch implementation details to be a bit lacking
(and my x86 foo ain't great).  So after pounding out support for
the Blackfin arch, start documenting the requirements/details.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
LKML-Reference: <1252973415-21264-1-git-send-email-vapier@gentoo.org>
Acked-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/Kconfig

@@ -11,12 +11,18 @@ config NOP_TRACER
 
 config HAVE_FTRACE_NMI_ENTER
 	bool
+	help
+	  See Documentation/trace/ftrace-implementation.txt
 
 config HAVE_FUNCTION_TRACER
 	bool
+	help
+	  See Documentation/trace/ftrace-implementation.txt
 
 config HAVE_FUNCTION_GRAPH_TRACER
 	bool
+	help
+	  See Documentation/trace/ftrace-implementation.txt
 
 config HAVE_FUNCTION_GRAPH_FP_TEST
 	bool
@@ -28,21 +34,25 @@ config HAVE_FUNCTION_GRAPH_FP_TEST
 config HAVE_FUNCTION_TRACE_MCOUNT_TEST
 	bool
 	help
-	 This gets selected when the arch tests the function_trace_stop
-	 variable at the mcount call site. Otherwise, this variable
-	 is tested by the called function.
+	  See Documentation/trace/ftrace-implementation.txt
 
 config HAVE_DYNAMIC_FTRACE
 	bool
+	help
+	  See Documentation/trace/ftrace-implementation.txt
 
 config HAVE_FTRACE_MCOUNT_RECORD
 	bool
+	help
+	  See Documentation/trace/ftrace-implementation.txt
 
 config HAVE_HW_BRANCH_TRACER
 	bool
 
 config HAVE_SYSCALL_TRACEPOINTS
 	bool
+	help
+	  See Documentation/trace/ftrace-implementation.txt
 
 config TRACER_MAX_TRACE
 	bool