minor changes for port-prep

Two new additions for port PReP:

1) The build scripts can now generate a bootable ISO image, so it is now
possible to boot and install from CD.  The CD is currently built with the com0
bootloader, so it is serial-console only.

2) There is now a driver for the floppy drive/controller.  Additionally, isadma
now works, so in theory, the builtin audio can now be supported.  However, I'm
not very good with audio drivers, and haven't had much luck with it.

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Tim Rightnour <[email protected]>
NetBSD: Free multi-architecture OS http://www.netbsd.org/
Genecys: Open Source 3D MMORPG: http://www.genecys.org/