This allows multiple gPXE ROMs in a system to be disambiguated at boot
time; the PCI ID will show up in the boot menu for a BBS-compliant BIOS.

Move the printing functions from pxeprefix.S into libprefix.S, so they
are available for debug from any prefix.

clean separation between loading and starting, but does mean that more
PXE stacks survive the process.

addresses if the signature checks fail.

we can never return to the PXE stack and must always use INT 18.

Record all information required for populating a struct undi_device.

Make debugging output more human-readable.

and call UNDI_SHUTDOWN first to make sure the NIC is in a safe state.

memory (unless we get an error while stopping the base code).  Leave UNDI
resident (though stopped) for .kpxe.

Still need to add code to record the device identification parameters
prior to stopping UNDI.

mechanism has changed anyway, and so must be rewritten, but at least doing
this makes the output of "make symcheck" more legible.