[S390] sparse: fix sparse warnings about missing prototypes

Add prototypes and includes for functions used in different modules.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
diff --git a/arch/s390/kernel/suspend.c b/arch/s390/kernel/suspend.c
index b6f9afe..47df775 100644
--- a/arch/s390/kernel/suspend.c
+++ b/arch/s390/kernel/suspend.c
@@ -7,6 +7,7 @@
  */
 
 #include <linux/pfn.h>
+#include <linux/suspend.h>
 #include <linux/mm.h>
 #include <asm/system.h>