Make textdump work:

 - Use first swap partition for dumping.  On crash, the system will
   be able to override GELI provider and write directly on the
   underlying device.

 - When the system runs ix-fstab for the first time, do a fsck and
   mount /data read-write.  If there is any crash dump available,
   save it before proceeding to do swap, etc.

(cherry picked from commit 5ea1a9128e0fb825f9b3ec1f6196755868add022)