Add kernel/notifier.c

There is separate notifier header, but no separate notifier .c file.

Extract notifier code out of kernel/sys.c which will remain for
misc syscalls I hope. Merge kernel/die_notifier.c into kernel/notifier.c.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/notifier.h b/include/linux/notifier.h
index bd37880..6ec7e21 100644
--- a/include/linux/notifier.h
+++ b/include/linux/notifier.h
@@ -240,5 +240,7 @@
 #define KBD_KEYSYM		0x0004 /* Keyboard keysym */
 #define KBD_POST_KEYSYM		0x0005 /* Called after keyboard keysym interpretation */
 
+extern struct blocking_notifier_head reboot_notifier_list;
+
 #endif /* __KERNEL__ */
 #endif /* _LINUX_NOTIFIER_H */