Fixed rc and fstab configurations to allow device encryption

Detailed description:
   fstab entries were set up to encrypt using a footer at the end of the
partition, but the fs was not recognized by cryptfs.c as being
appropriately shortened.  Inspection of the original fstab.m7 reveals
crypt keys are stored on the "extra" block, or /dev/block/mmcblk0p27,
changed fstab to match.
   tmpfs mountpoints inside /data prevented cryptfs from unmounting /data.
Fixed this by assigning mountpoints to directories inside /mnt and
creating symbolic links to /mnt inside /data.

Change-Id: I22b390bc7e329b3f79ac3b73e02bd0c33c4b1025