s390: make various functions static, add declarations to header files

Make various functions static, add declarations to header files to
fix a couple of sparse findings.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
diff --git a/arch/s390/mm/maccess.c b/arch/s390/mm/maccess.c
index 921fa54..d1e0e0c 100644
--- a/arch/s390/mm/maccess.c
+++ b/arch/s390/mm/maccess.c
@@ -14,6 +14,7 @@
 #include <linux/gfp.h>
 #include <linux/cpu.h>
 #include <asm/ctl_reg.h>
+#include <asm/io.h>
 
 /*
  * This function writes to kernel memory bypassing DAT and possible