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/MetadataCrypt.cpp b/MetadataCrypt.cpp
index 0934563..e156424 100644
--- a/MetadataCrypt.cpp
+++ b/MetadataCrypt.cpp
@@ -194,11 +194,11 @@
     return true;
 }
 
-bool e4crypt_mount_metadata_encrypted(const std::string& mount_point, bool needs_encrypt) {
-    LOG(DEBUG) << "e4crypt_mount_metadata_encrypted: " << mount_point << " " << needs_encrypt;
+bool fscrypt_mount_metadata_encrypted(const std::string& mount_point, bool needs_encrypt) {
+    LOG(DEBUG) << "fscrypt_mount_metadata_encrypted: " << mount_point << " " << needs_encrypt;
     auto encrypted_state = android::base::GetProperty("ro.crypto.state", "");
     if (encrypted_state != "") {
-        LOG(DEBUG) << "e4crypt_enable_crypto got unexpected starting state: " << encrypted_state;
+        LOG(DEBUG) << "fscrypt_enable_crypto got unexpected starting state: " << encrypted_state;
         return false;
     }
     auto data_rec = fs_mgr_get_entry_for_mount_point(fstab_default, mount_point);