kset: convert /sys/power to use kset_create

Dynamically create the kset instead of declaring it statically.  We also
rename power_subsys to power_kset to catch all users of the variable and
we properly export it so that people don't have to guess that it really
is present in the system.

The pseries code is wierd, why is it createing /sys/power if CONFIG_PM
is disabled?  Oh well, stupid big boxes ignoring config options...

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

kernel/power/power.h

@@ -63,8 +63,6 @@ static struct subsys_attribute _name##_attr = {	\
 	.store	= _name##_store,		\
 }
 
-extern struct kset power_subsys;
-
 /* Preferred image size in bytes (default 500 MB) */
 extern unsigned long image_size;
 extern int in_suspend;