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/include/linux/magic.h b/include/linux/magic.h
index 5b4e28b..927138c 100644
--- a/include/linux/magic.h
+++ b/include/linux/magic.h
@@ -9,6 +9,7 @@
 #define DEBUGFS_MAGIC          0x64626720
 #define SYSFS_MAGIC		0x62656572
 #define SECURITYFS_MAGIC	0x73636673
+#define SELINUX_MAGIC		0xf97cff8c
 #define TMPFS_MAGIC		0x01021994
 #define SQUASHFS_MAGIC		0x73717368
 #define EFS_SUPER_MAGIC		0x414A53