Config.in: Add BR2_DEPRECATED_SINCE_2015_08

In preparation for the deprecation of certain features in 2015.08, add
the BR2_DEPRECATED_SINCE_2015_08 symbol.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

Config.in

@@ -312,6 +312,10 @@ config BR2_DEPRECATED_SINCE_2015_05
 	bool
 	default y
 
+config BR2_DEPRECATED_SINCE_2015_08
+	bool
+	default y
+
 endif
 
 config BR2_ENABLE_DEBUG