PM: Add user-space wake lock api.

This adds /sys/power/wake_lock and /sys/power/wake_unlock.
Writing a string to wake_lock creates a wake lock the
first time is sees a string and locks it. Optionally, the
string can be followed by a timeout.
To unlock the wake lock, write the same string to wake_unlock.

Change-Id: I66c6e3fe6487d17f9c2fafde1174042e57d15cd7
diff --git a/kernel/power/main.c b/kernel/power/main.c
index dad38e2..ff29679 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -308,6 +308,11 @@
 
 #endif /* CONFIG_PM_TRACE */
 
+#ifdef CONFIG_USER_WAKELOCK
+power_attr(wake_lock);
+power_attr(wake_unlock);
+#endif
+
 static struct attribute * g[] = {
 	&state_attr.attr,
 #ifdef CONFIG_PM_TRACE
@@ -320,6 +325,10 @@
 #ifdef CONFIG_PM_DEBUG
 	&pm_test_attr.attr,
 #endif
+#ifdef CONFIG_USER_WAKELOCK
+	&wake_lock_attr.attr,
+	&wake_unlock_attr.attr,
+#endif
 #endif
 	NULL,
 };