[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/process.c b/arch/s390/kernel/process.c
index 5e64a9a..9451b21 100644
--- a/arch/s390/kernel/process.c
+++ b/arch/s390/kernel/process.c
@@ -12,6 +12,7 @@
 #include <linux/sched.h>
 #include <linux/kernel.h>
 #include <linux/mm.h>
+#include <linux/elfcore.h>
 #include <linux/smp.h>
 #include <linux/slab.h>
 #include <linux/interrupt.h>