makefs(8): DragonFly porting.

makefs(8): DragonFly porting.

Some notes:

* UFS2 support has been disabled for now. It would require more UFS2
  related pieces in our UFS kernel headers. I might look at enabling
  this in the future.

* Our CGSIZE() macro causes issues when used in makefs(8), which is
  why I'm using FreeBSD's currently.

* makefs(8) uses a local daddr_t type which is 64 bits wide, since
  ours is 32 bits.

* I added cg_blks() and cg_blktot() calls in a few places because
  our fsck(8) checks them in pass 5. I'm not sure if the associated
  fields are actually needed anymore.