power management: change /sys/power/disk display

Change /sys/power/disk to display all valid modes as well as the currently
selected one in a fashion known from the LED subsystem.

This changes userspace API, but it is apparently not used much (we asked
some userspace developers)

Signed-off-by: Johannes Berg <johannes@sipsolutions.net>
Acked-by: "Rafael J. Wysocki" <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/power/interface.txt b/Documentation/power/interface.txt
index 8c5b41b..fd5192a 100644
--- a/Documentation/power/interface.txt
+++ b/Documentation/power/interface.txt
@@ -34,8 +34,12 @@
 we are able to look in the log messages and work out, for example, which code
 is being slow and which device drivers are misbehaving.
 
-Reading from this file will display what the mode is currently set
-to. Writing to this file will accept one of
+Reading from this file will display all supported modes and the currently
+selected one in brackets, for example
+
+	[shutdown] reboot test testproc
+
+Writing to this file will accept one of
 
        'platform' (only if the platform supports it)
        'shutdown'