makefs: add copies of NetBSD makefs msdos source files

We do not treat makefs as contrib code. Import copies of makefs msdos
files from NetBSD so that we can track our changes to these files.

These are copied from NetBSD, with only a change to use FBSDID and
$FreeBSD$ instead of KERNEL_RCSID and $NetBSD$. A copy of the
original $NetBSD$ tag remains in each source file.

Submitted by: Siva Mahadevan
Sponsored by: The FreeBSD Foundation