Add BR2_DEPRECATED_SINCE_2014_08

In preparation for the deprecation of certain features in 2014.08, add
the BR2_DEPRECATED_SINCE_2014_08 symbol.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
diff --git a/Config.in b/Config.in
index bf1ca86..50968fb 100644
--- a/Config.in
+++ b/Config.in
@@ -319,6 +319,10 @@
 	bool
 	default y
 
+config BR2_DEPRECATED_SINCE_2014_08
+	bool
+	default y
+
 endif
 
 config BR2_ENABLE_DEBUG