PM / Sleep: Add "prevent autosleep time" statistics to wakeup sources

Android uses one wakelock statistics that is only necessary for
opportunistic sleep.  Namely, the prevent_suspend_time field
accumulates the total time the given wakelock has been locked
while "automatic suspend" was enabled.  Add an analogous field,
prevent_sleep_time, to wakeup sources and make it behave in a similar
way.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/ABI/testing/sysfs-devices-power

@@ -158,6 +158,17 @@ Description:
 		not enabled to wake up the system from sleep states, this
 		attribute is not present.
 
+What:		/sys/devices/.../power/wakeup_prevent_sleep_time_ms
+Date:		February 2012
+Contact:	Rafael J. Wysocki <rjw@sisk.pl>
+Description:
+		The /sys/devices/.../wakeup_prevent_sleep_time_ms attribute
+		contains the total time the device has been preventing
+		opportunistic transitions to sleep states from occuring.
+		This attribute is read-only.  If the device is not enabled to
+		wake up the system from sleep states, this attribute is not
+		present.
+
 What:		/sys/devices/.../power/autosuspend_delay_ms
 Date:		September 2010
 Contact:	Alan Stern <stern@rowland.harvard.edu>