kernel: fix enabling coredump support on 3.7+

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@35123 3c298f89-4303-0410-b956-a3cf2f4a3e73

Config.in

@@ -276,8 +276,12 @@ menu "Global build settings"
 		bool "Compile the kernel with SysRq support"
 		default y
 
+	config KERNEL_COREDUMP
+		bool
+
 	config KERNEL_ELF_CORE
 		bool "Enable process core dump support"
+		select KERNEL_COREDUMP
 		default y
 
 	config KERNEL_PROVE_LOCKING