parisc: Add full PDC firmware boot menu

Finally add the real boot menu.
If qemu is started with the "-boot menu=on" option, the PDC boot menu is
shown and the user can then boot any of the available SCSI disc/CDs.
Just type "BOOT" (to boot the default device), or "BOOT FWSCSI.4" (to boot
SCSI device #4).

Signed-off-by: Helge Deller <deller@gmx.de>
4 files changed