Support metadata encryption

Bug: 29189559
Test: Angler, Marlin build and boot
Change-Id: Ia7b070781f5f16ff8bfd934569a2209c80c28385
diff --git a/fs_mgr/fs_mgr_priv.h b/fs_mgr/fs_mgr_priv.h
index c985462..3ca507b 100644
--- a/fs_mgr/fs_mgr_priv.h
+++ b/fs_mgr/fs_mgr_priv.h
@@ -107,6 +107,7 @@
 #define MF_ERASEBLKSIZE     0x800000
 #define MF_LOGICALBLKSIZE  0X1000000
 #define MF_AVB             0X2000000
+#define MF_KEYDIRECTORY 0X4000000
 
 #define DM_BUF_SIZE 4096