kernfs: add CONFIG_KERNFS

As sysfs was kernfs's only user, kernfs has been piggybacking on
CONFIG_SYSFS; however, kernfs is scheduled to grow a new user very
soon.  Introduce a separate config option CONFIG_KERNFS which is to be
selected by kernfs users.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/fs/sysfs/Kconfig b/fs/sysfs/Kconfig
index 8c41fea..b275601 100644
--- a/fs/sysfs/Kconfig
+++ b/fs/sysfs/Kconfig
@@ -1,6 +1,7 @@
 config SYSFS
 	bool "sysfs file system support" if EXPERT
 	default y
+	select KERNFS
 	help
 	The sysfs filesystem is a virtual filesystem that the kernel uses to
 	export internal kernel objects, their attributes, and their