celox: enable whole disk encryption

  * add the encryptable footer to the /data partition
  * stop mounting the special /data/tombstones partition
    - this mount prevents cryptfs from unmounting /data to prepare for encryption
    - instead, allow tombstones to be written to /data/tombstones directly
    - this matches how newer skyrocket stock roms and d2 handle tombstones

Change-Id: I108bd8912fb7ab06d1413623cb0ba477fb0a065a