swsusp: free more memory

Move the definition of PAGES_FOR_IO to kernel/power/power.h and introduce
SPARE_PAGES representing the number of pages that should be freed by the
swsusp's memory shrinker in addition to PAGES_FOR_IO so that device drivers
can allocate some memory (up to 1 MB total) in their .suspend() routines
without causing the suspend to fail.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Pavel Machek <pavel@ucw.cz>
Cc: Nigel Cunningham <nigel@nigel.suspend2.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/kernel/power/swsusp.c b/kernel/power/swsusp.c
index 1109023..5da304c 100644
--- a/kernel/power/swsusp.c
+++ b/kernel/power/swsusp.c
@@ -233,7 +233,7 @@
 		long size, highmem_size;
 
 		highmem_size = count_highmem_pages();
-		size = count_data_pages() + PAGES_FOR_IO;
+		size = count_data_pages() + PAGES_FOR_IO + SPARE_PAGES;
 		tmp = size;
 		size += highmem_size;
 		for_each_zone (zone)