SELinux: move SELINUX_MAGIC into magic.h

The selinuxfs superblock magic is used inside the IMA code, but is being
defined in two places and could someday get out of sync.  This patch moves the
declaration into magic.h so it is only done once.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index a7be3f0..ca83579 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -8,14 +8,13 @@
 #ifndef _SELINUX_SECURITY_H_
 #define _SELINUX_SECURITY_H_
 
+#include <linux/magic.h>
 #include "flask.h"
 
 #define SECSID_NULL			0x00000000 /* unspecified SID */
 #define SECSID_WILD			0xffffffff /* wildcard SID */
 #define SECCLASS_NULL			0x0000 /* no class */
 
-#define SELINUX_MAGIC 0xf97cff8c
-
 /* Identify specific policy version changes */
 #define POLICYDB_VERSION_BASE		15
 #define POLICYDB_VERSION_BOOL		16