vold: allow specifying HEH filenames encryption

Make the vold changes needed to support specifying aes-256-heh filenames
encryption.  The previous mode, aes-256-cts, remains supported as well.

The file /data/unencrypted/mode is updated to have the syntax
contents_encryption_mode[:filenames_encryption_mode] instead of just
contents_encryption_mode.  This is consistent with the new fstab syntax.

Bug: 34712722
Change-Id: Ibc236d0ec4fdeda4e4e301f45fb996317692cfa3
3 files changed