[S390] Fix a lot of sparse warnings.

Most noteable part of this commit is the new local header file entry.h
which contains all the function declarations of functions that get only
called from asm code or are arch internal. That way we can avoid extern
declarations in C files.
This is more or less the same that was done for sparc64.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
diff --git a/drivers/s390/cio/device.h b/drivers/s390/cio/device.h
index d40a2ff..cb08092 100644
--- a/drivers/s390/cio/device.h
+++ b/drivers/s390/cio/device.h
@@ -127,4 +127,5 @@
 void retry_set_schib(struct ccw_device *cdev);
 void cmf_retry_copy_block(struct ccw_device *);
 int cmf_reenable(struct ccw_device *);
+extern struct device_attribute dev_attr_cmb_enable;
 #endif