init: Unregister filesystem upon exit

Fixes a panic that occurs upon the second module loading of the
filesystem. The filesystem did not ungresiter itself, and failed
to load properly upon subsequent attempts.

Also added some debug statements to show progression of initialization
and registration.
vvfs.h: Added header with superblock definition

Added the local vvfs header, with a definition for what will be the
the on disk version of the superblock.