swsusp: do not use page flags

Make swsusp use memory bitmaps instead of page flags for marking 'nosave' and
free pages.  This allows us to 'recycle' two page flags that can be used for
other purposes.  Also, the memory needed to store the bitmaps is allocated
when necessary (ie.  before the suspend) and freed after the resume which is
more reasonable.

The patch is designed to minimize the amount of changes and there are some
nice simplifications and optimizations possible on top of it.  I am going to
implement them separately in the future.

Signed-off-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>

kernel/power/main.c

@@ -244,6 +244,7 @@ static int enter_state(suspend_state_t state)
 	return error;
 }
 
+#ifdef CONFIG_SOFTWARE_SUSPEND
 /*
  * This is main interface to the outside world. It needs to be
  * called from process context.
@@ -252,6 +253,7 @@ int software_suspend(void)
 {
 	return enter_state(PM_SUSPEND_DISK);
 }
+#endif
 
 
 /**