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 fut

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.

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Bring in most of makefs(8) from FreeBSD unchanged.

To create filesystem images without kernel involvement. We can use it
to create our initrd without needing vn(4).

Originally from NetBSD.