vold: rename from "ext4 encryption" to fscrypt

We support file-based encryption on both ext4 and f2fs now, and the
kernel API is the same.  So rename things appropriately in vold:

    e4crypt => fscrypt
    ext4enc => fscrypt
    Ext4Crypt => FsCrypt
    EXT4_* => FS_*
    ext4_encryption_key => fscrypt_key

Additionally, the common functions shared by 'vold' and 'init' are now
in libfscrypt rather than ext4_utils.  So update vold to link to
libfscrypt and include the renamed headers.

Note: there's a chance of 'fscrypt' being confused with the dm-crypt
based encryption code in vold which is called 'cryptfs'.  However,
fscrypt is the name used in the kernel for ext4/f2fs/ubifs encryption,
and it's preferable to use the same name in userspace.

Test: built, booted device with f2fs encryption
Change-Id: I2a46a49f30d9c0b73d6f6fe09e4a4904d4138ff6
diff --git a/model/Disk.cpp b/model/Disk.cpp
index 2b6773d..3d25e4c 100644
--- a/model/Disk.cpp
+++ b/model/Disk.cpp
@@ -15,7 +15,7 @@
  */
 
 #include "Disk.h"
-#include "Ext4Crypt.h"
+#include "FsCrypt.h"
 #include "PrivateVolume.h"
 #include "PublicVolume.h"
 #include "Utils.h"
@@ -28,7 +28,7 @@
 #include <android-base/properties.h>
 #include <android-base/stringprintf.h>
 #include <android-base/strings.h>
-#include <ext4_utils/ext4_crypt.h>
+#include <fscrypt/fscrypt.h>
 
 #include "cryptfs.h"