kset: convert /sys/devices to use kset_create

Dynamically create the kset instead of declaring it statically.  We also
rename devices_subsys to devices_kset to catch all users of the
variable.

Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/base/base.h b/drivers/base/base.h
index 10b2fb6..7e309a4 100644
--- a/drivers/base/base.h
+++ b/drivers/base/base.h
@@ -44,4 +44,4 @@
 
 extern int devres_release_all(struct device *dev);
 
-extern struct kset devices_subsys;
+extern struct kset *devices_kset;