Comment 53 for bug 8497

These two comments suggest EDD is the right way to construct device.map:

http://kerneltrap.org/node/6408
        "These days, you just cannot enumerate controllers in any meaningful manner.
        I don't think you ever really could, but at least with static hardware,
        any random enumeration was as good as any other."

http://lwn.net/Articles/75923/
        Say Y or M here if you want to enable BIOS Enhanced Disk Drive
        Services real mode BIOS calls to determine which disk
 BIOS tries boot from. This information is then exported via driverfs.

        This option is experimental, but believed to be safe,
        and most disk controller BIOS vendors do not yet implement this feature.

Since the main purpose of device.map is to tell the stage1 GRUB code which disk to look on for the stage2, and the disk address seems to be resolved by the BIOS, we really need to be asking the BIOS for this information.