[syslinux] chainload cdrom

[aaron.mcsorley at amd.com]

There are two methods I'm playing with, booting sbm with memdisk and 
booting comboot sbm as a kernel.
I can boot sbm from pxelinux and then select cdrom boot with both ways but,
with the comboot sbm the cdrom that is booting locks up. The memdisk method
does work. I also have a dvdrom that sbm wont boot but, thats another topic.
I would prefer to use the comboot kernel method. 
This would be really great if there were a comboot example that uses just the 
cdrom boot part of sbm without the sbm menu.

I also wonder if this eltorito stack could be used to boot a 
cdrom image from pxelinux, that would be another really nice thing.

label cdrommem
        kernel memdisk
        append initrd=sbm.bin

label cdromkern
        kernel sbm.cbt