SECURITY must depend on SYSFS

CONFIG_SECURITY=y and CONFIG_SYSFS=n results in the following compile error:

<-- snip -->

...
LD vmlinux
security/built-in.o: In function `securityfs_init':
inode.c:(.init.text+0x1c2): undefined reference to `kernel_subsys'
make: *** [vmlinux] Error 1

<-- snip -->

@@ -35,6 +35,7 @@
 
 config SECURITY
 	bool "Enable different security models"
+	depends on SYSFS
 	help
 	  This allows you to choose different security modules to be
 	  configured into your kernel.