tracing/function-graph-tracer: enabled by default

CONFIG_FUNCTION_GRAPH_TRACER depends on FUNCTION_TRACER already,
(turning it non-default) so it so making it default-n is pointless.

So enable it by default - it's a nice extension of the function tracer.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/Kconfig

diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index 8b6b673..bde6f03 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -67,6 +67,7 @@
 	bool "Kernel Function Graph Tracer"
 	depends on HAVE_FUNCTION_GRAPH_TRACER
 	depends on FUNCTION_TRACER
+	default y
 	help
 	  Enable the kernel to trace a function at both its return
 	  and its entry.